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The Decl ine and Fa ll o f the R om an D e n a r i u sA l a n W . P e n s eProvos t and V i ce Pres i den t , Leh i gh U n i ve r s i t y , Be t h lehem , P A 18015- 3035

The basic silver coin of the early Roman Empire was the denar i us . By decree of CaesarAugustus in 15 B.C.E., it was nearly pure silver, 95%-98%, and had a fixed weight andvalue in relationship to the rest of the Roman mone tar y system. Ov er the next 270 years,the silver content of the denar i us declined gradually and then precipitously to about 2%.This degradation occurred more rapidly in the provinces than in Rome. The microstruc-tures of a series of Roman denar i i taken from this time period are used to illustrate thesechanges.

The final stage of the denar i us was a duplex plated coin with a nearly copper core anda silver surface. This produced a lower-cost coin with an apparent value equal to theprevious ones. Eventually, the surface coating was so thin that it quickly rubbed off afterthe coin left the mint. By this time (280 C.E.), the silver coinage of the empire had almos ttotally lost its value and had to be reconst ituted by Diocletion. Among the coins stud iedis an early duplex plated denar i us of Caesar Augustus, probably an early forgery produc edduring his lifetime in clear violation of his edict.

I N T R O D U C T I O N

The coinage of the Ro man Empire, even inits early periods, was relatively consistentand orderly. By 269 B.C.E. [1], it was basedprimarily on silver and copper coins, al-though gold coins also were occasionallyminted. The original copper coinage wasweight based, and was related to theRoman pound, the libra, which was about325 g. The basic copper coin, the as, wasto weigh 1 Roman pound. This was a castcoin of some size and subdivisions of theas were used, as will be described later. Thecopper coins are of note because the ghostof this unit is to be found in the Britishmonetary system, which still uses thepound, abbreviated as .

The other fundamental Roman mone-tary unit was the denar i us . This was a silvercoin initially wort h 10 asses, but eventuallyequal to 16 asses. There were intermediatebrass coins, the ses ter t ius , four of whichequaled one denar i us (equal to four asses),

213

and the depond i us , which was equal to twoasses. The denar i us also lives on today, aftera sort, in the British system of coinage asthe abbreviation used for the pence, "d."The gold coin, when issued, was the a u -reus , and was equal to 25 denar i i , or thequ i nar i us , equal to 12 denar i i .While the as was a cast coin in the earlypart of this period, it was an inconvenientunit and did not facilitate trade with theeconomic world of the time, which alreadyused struck coinage. Thus, the smaller de-nominat ions were all wro ugh t coins, as theas itself became, in time, as its size andweight decreased over the next 200 years.

By the time of Juhus Caesar, the sy stemwas badly out of control. The as hadshrun k to one Roman ounce @2 l ibra) , andCaesar Augus tus (Octavian) in 15 B.C.E. es-tablished monetary decrees that stabilizedthe system [2]. The relationship betweenthe coins remained as described earlier,but the aureus was set at 7.5g, the denar i usat 3.9g, the as at 10g, and the ses ter t ius at

( O E ls e vi er S c i e n c e P u b l i s h i n g C o . , I n c ., 1 9 92 M A T E R I A L S C H A R A C T E R I Z A T I O N 2 9 : 2 1 3 - 2 2 2 ( 19 9 2 )6 5 5 A v e n u e o f t h e A m e r i c a s , N e w Y o r k , N Y 1 0 0 10 1 0 4 4 - 5 8 0 3 / 9 2 /$ 5 . 0 0

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214 A. W. Pense24g (not at 40g, as might be supposed).This was not necessarily intrinsic valuecoinage, because the metal value betweensilver and copper was about 240 to 1.

T H E R O M A N DENARIUST h e b a s ic Ro m a n s i l ve r co i n , a s d e sc r i b e dearlier, was the denar ius . In size, it was alittle larger than a dime, about 20mmdiam., and in the republican and early em-pire period was of a high level of fineness(purity), about 95 wt.%-98 wt.% silver.This was maintained through the reformof Augustus. To provide an idea of thevalue of this coin to Romans, a Romanarmy private in the time of Augustusearned be tween 200 and 300 denar i i a year,paid every 4 months. An officer could earn10,000 per year; a high officer, as much as25,000 [3]. As is true of military bureau-cracies everywhere, the private never sawmuch of it. Because he had to pay a num berof deductions for food, uniforms, and evenfuneral expenses, should he not survive toretirement, he finally received only 15-20each payd ay- -an d the next payday was 4months away!

The attraction of service in the army was,at first, not mon eta ry but patriotic. As timepassed, the army was increasingly madeup of career soldiers. By the time of Au-gustus, the army numbered about 250,000men, almost all in the army for life. Thebenefits were a steady, if hard, job; food;clothing; shelter; and a retirement after 20or 25 years with an a llotment of land (usu-ally in a province). It included Roman cit-izenship (if the soldier did not already havethis). In the Empire period, the last was anattraction because the Italian Roman Le-gions were gradually supplemented bylarge numbers of auxiliary forces drawnfrom conquered provinces. For these, cit-izenship was to be desired, not only forthemselves, but for their children, becausemany were stationed more or less perma-nently on their own frontier and had fam-ilies there.Relating the d e n a r i u s to the pay of thearmy is of great practical significance. The

pressure of supporting, increasing, andeventual ly keeping the political favor of thelegions became one of the primary reasonsfor debasement of the denar ius . Other rea-sons included maintaining the imperiallifestyle, providing for public works andentertainments, and supporting grain im-ports. In the Later Empire, after 200 c.E.,emperors ruled only through the supportof the army, which now numbered500,000. As the army deman ded more an dmore for its maintenance, a very significantpressure was created for more coinagethan there was bullion metal to support.Paying, or more accurately, paying off, thearmy was the name of the game. (Duringone 67-year period, there were 29 emper-ors, only 4 of whom died of naturalcauses.) The need for money was acute.The solution that quickly suggested itselfwas simply debasing the silver denar iuswith copper, a process that started in the1st Centu ry and increased for the next two.C O I N P R O D U C T I O N A N D A V A I L A B I L I T YThe coinage of the Roman Republic wasunder the responsibility of designatedmoneyers, but the actual coins were pro-duced by a professional staff of skilledworkers. In the republican period, coinproduction was the responsibility of thesenate. With the birth of the Empire, theemperor took control of silver and goldcoinage and left only the copper coinageto the senate. The work was originallydone in association with the Temple of Mo-neta in Rome, but mints were later estab-lished in major cities in the provinces. Thesenate had given its military generals theright to mint coins to pay their troops inthe 2nd Century B.C.E., SO the mint alsotraveled with the army in some cases.

Die engraving and manufacturing ofcoins were already long-established tech-nologies [1] by the time of the Roman Em-pire. Dies were made of iron and high tinbronzes, and coins were struck by hand,i.e., each coin blank was hea ted and struckindividually between a hand-held up perdie with the "reverse" pattern, usually a

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Decline and F all of the Rom an Denarius 2 1 5god, a goddess, or a symbol, and a sta-tionary lower die, with the "obverse" orportrait pattern. There was generally noparticular angular orientation relationshipbetween the two patterns. The blanks wereusually cast in round flat molds. Becausethe priority at the mint was on produc tionand not quality, the coins were not nec-essarily centered or well struck, althoughweights and compositions were relativelyuniform at any time and location.It is these latter characteristics that havemade it possible to study the debasementof the denar iu s over time, even with only arelatively limited number of samples. Thenumber of available samples is not small,however. If you consider the whole armyof legionnaires and auxiliaries at the timeof Augustus , 250,000 men, the total annua lrequirement of the army for silver denar i i(or equivalent copper coins) was at least75,000,000 per year! While there was con-siderable reuse of coins (some of whichwere melted do wn and later reissued) overa 500-year period, the number minted wasenormous. If I in 15,000 of these coins per-sists until today (as has been estimated),then the number of samples available forstudy from, say, a 10-year period, could beas many as 50,000. This is why coin auc-tions today with thousands of denar i i forsale are not uncommon, and a coin in rea-sonable, but not outstanding, condition("fine"), can be purchased for as little as$50.00 for an emperor who ruled a rela-tively long time and consequently had anumber of coins minted in his name.Poorer-quality denar i i (broken, corroded,scratched, cut) can be purchased for as lit-tle as $10.00. The cost rises rapidly withcondition and rarity, up to possibly severalhun dred thous and dollars. The key to pre-paring an article like this economically istherefore to select samples for study inpoorer condition from the commonemperors.

STUDIES OF THE DENARIUST h e r e h a v e b e e n m a n y s t u d ie s m a d e c o n -c e r n i n g a n c i e n t R o m a n c o i n a g e f r o m t h e

historical, artistic, philosophical, political,technological, and economic viewpoints.From the metallurgical viewpoint, someoutstanding studies and collections ofstudies have been produced. Importantamong these was a symposi um held by theroyal Numismatic Society in 1970 [4] deal-ing primarily with the chemical analysis ofcoins. Other comprehensive studies spe-cifically of the denar iu s are available, bothfrom the symposi um papers described pre-viously , and elsewhere [5]. This article pro-poses no such comprehensive study. Aswell demons trated in an article by Cope [61in the 1970 Symposium proceedings, atruly comprehensive study of debasementof coinage can only be unde rtaken using alarge num ber of samples and relatively so-phisticated chemical analysis techniques.The latter are required because of selectivecorrosion effects, differences in manufac-turing techniques, normal variation incomposition resulting from mint practice,and the tendency to use duplex coins inthe later empire period. Fortunately, theexcellent work on chemical analysis byCope and others has provided us a baseon which to stand and allows a usefulstudy even with a limited number ofsamples.The purpose of this article is to illustratethe results of changes in the minting stan-dards of the Roman denar iu s through se-lected examples. The emphasis is on mi-crostructure and what it can tell us aboutthe manufacture, composit ion, andchanges in these coins in their historicalcontext. Bulk chemical analysis was not at-tempted, although much about composi-tional changes can be unde rstood from mi-crostructure. Indeed, in some instances,bulk chemistry alone would be less help-ful. Microchemical methods were also notundertaken, and some reasons for notusing these techniques are listed in detailby Cope [6]. These primarily rest on thecomplexity of coin processing and corro-sion, which rendered the final local com-position of the coin quite diff erent from itsoriginal one. Microchemical analysiswould undoubtedly have added to the

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216 A. W. Penses t u d y , b u t i t w a s j u d g e d t h a t m i c r o st r u c-t u ra l a n a ly s is , s u p p l e m e n t e d b y th e p r io rc h e m i c a l a n a l y s i s s t u d i e s , w a s s u f f i c i e n t t ou n d e r s t a n d t h e m e a n s u s e d f o r t h e d e v a l-u a t i o n o f t h e denarius.

C O I N S ELEC TIO N A N D P R O C ED U RESF O R TH E S TU D Y

T h e c h e m i c a l a n a l y s i s r e c o r d f o r R o m a n s il-v e r c o i n s h a s b e e n f a i r l y w e l l e s t a b l i s h e da n d t h e r e s u l t s , s h o w n i n F ig . 1 , a r e a c o m -p o s i t e f r o m a n u m b e r o f s o u r c e s [2 , 5 , 6 ].B a s e d o n t h i s w o r k , t h e p r o c e d u r e i n c o i ns e l e c ti o n f o r t h is s t u d y w a s t o o b t a i n s o m er e p r e s e n t a t i v e s a m p l e s f r o m c r i t i c a l t i m ep e r i o d s i n t h e h i s t o r y o f t h e s i l v e r i s s u e st h a t w o u l d i l l u s t r a t e t h e r e p o r t e d c h a n g e si n s il v e r c o n t e n t . U l t i m a t e l y , 1 3 c o i n s w e r es e l e c t e d fo r s tu d y . T h e s e i n c l u d e d c o i n s f o rM . Tu l l i a (109 B .C .E.) ; Ju l i us Ca esa r (54 -51B.C .E.) ; A u g u s t u s (29 B .C .E. - -14 C .E.) ; N er o( 5 4 - 6 8 ) ; T i t u s ( 7 9 - 8 1 ) ; T r a j a n - - t w o c o i n s( 9 8 -1 1 8 ) ; F a u s t i n a I, w i f e o f A n t o n i u s P i u s( 1 3 8 - 1 4 1 ) ; C a r aca l l a ( 2 1 1 - 2 1 7 ) ; S ev e r u sA l e x a n d e r ( 2 2 2 - 2 3 5 ) ; T r a j a n D e c i u s ( 2 4 9 -2 5 1 ) ; P o s t u m u s ( 2 5 9 - 2 6 8 ) ; a n d A u r e l i a n( 2 7 0 - 2 7 5 ) .

T h e p o s i t i o n i n t im e o f t h e s e c o i n s , in -d i ca t ed i n F i g . 1 , s p an s t h e l a t e r ep u b l i c( T u l l i a ) t o j u s t b e f o r e t h e m o n e t a r y r e f o r mo f D i o c l e t i o n ( 28 6). T h e y a r e i n t e n d e d t oc o r r e s p o n d t o r e p o r t e d c h a n g e i n c o m p o -s i t i o n a n d a l s o t o c o n f i r m t h e p e r i o d s o fr e l a t i v e c o n s t a n c y i n f i n e n e s s . T h e f i n e -n e s s o f t h e denarius d e c l i n e s g r a d u a l l y f r o mT u l li a t h r o u g h C a e s a r , N e r o , T i t u s, a n d

I0 0 ~ ~ j I i~ i i i

~ 60o

>

2o ~ ~ ~ ~ ~ ~

-1 O0 5o 0 50 1O0 15o 200 250 300BCE YEAR OF MINT ING CE

F I G . 1 . T h e c h a n g i n g s i l v e r c o n t e n t o f t h e denarius.

T r a j a n u p t o t h e t i m e o f A n t o n i u s P l u s ,a f t e r w h i c h i t s t a r t s a s h a r p d e c l i n e t o t h el ev e l ch a r ac t e r i s t i c o f t h e co i n s o f C a r aca l la .T h e n e x t d r o p c o r r e s p o n d s t o th e r e ig n s o fT r a ja n D e c i u s , P o s t u m u s , a n d f in a ll y A u -r e l i a n . T h e c o i n s s e l e c t e d s h o u l d s h o w b yt h e i r m i c r o s t r u c t u r e t h e g r a d u a l d e c l i n eo v e r 2 50 y e a r s , a n d t h e n t h e p r e c i p i t o u sd r o p o v e r t h e n e x t 1 0 0 y e a r s .

W e a r e a i d e d i n t h i s a n a l y s i s b y t h e f a c tt h a t th i s w a s b a s ic a ll y A g - C u c o i n a g e a n db y t h e n a t u r e o f t h e A g - C u s y s t e m (F ig .2 ) . Th i s i s a s i mp l e eu t ec t i c s y s t em, w i t hs o m e s o l i d s o l u b il i ty o n e a c h e n d o f t h ed i a g r a m . T h u s , t h e n e a r l y p u r e A g T u l li adenarius s h o u l d b e a s o l i d s o l u t i o n a l l o y ,b u t c o i n s w i t h m o r e t h a n 9 w t . % (1 5 a t .% )C u s h o u l d b e w i t h i n t h e e u t e c t i c r e g i o n . I fo n e a s s u m e s t h e c o i n b l a n k s w e r e c a s t a n dw e r e n o t a b l e t o c o m e t o e q u i l i b r i u m a t al o w e r te m p e r a t u r e , m i c r o s t r u c t u r e c a n b eu s e d t o e s t i m a t e p o s i t i o n in t h e p h a s e d ia -g r a m , a n d t h u s , r o u g h l y , c o m p o s i t i o n .T h i s w a s d o n e b y p o i n t c o u n t i n g f i e ld sf r o m t h e s p e c i m e n s t o d e t e r m i n e p e r c e n t -a g e o f p r i m a r y p h a s e a n d e u t e c ti c o r t h ea m o u n t s o f e a c h p h a s e . T h e e q u i li b r iu ma s s u m p t i o n m a y n o t b e e n t i r e l y a c c u r a t e ,b e c a u s e w e h a v e s o m e r e a s o n t o b e l i e v et h e c o i n b l a n k s w e r e r e h e a t e d f o r s t r i k i n g ,b u t i t i s s t i l l a r ea s o n ab l e o n e f o r t h e p u r -p o s e s o f t h is a n a l y s i s . A s w i ll b e s e e n , t h ec a s t s t r u c t u r e a p p e a r s t o h a v e c o m et h r o u g h t h e s t r i k in g p r o c e s s s u b s t a n t i a l l yu n a l t e r e d i n m a n y i n s t a n c e s .

T h e c o in s w e r e p r e p a r e d u s i n g s t a n d a rdm e t a l l o g r a p h ic t e c h n i q u e s . T h e s e in -c l u d e d , fo r m o s t sa m p l e s , m o u n t i n g a n dg r i n d i n g t h r o u g h 6 0 0 g r it S i C p a p e r , p o l -i s h in g w i t h 6 t~ m d i a m o n d f o l lo w e d b y 0 . 3I~m A 1 2 0 3 o r 1 t~ m d i a m o n d a n d f i n is h i n gb y v i b r a t o r y p o l i s h i n g w i t h S i O 2 . F o r t h eC u - A g a l lo y s a m p l e s , f e rr ic c h lo r i d e e tc h -a n t w a s e f f e c t i v e , a s w a s 2 % n i t a l w i t h t h eh i g h C u s a m p l e s . T h e h i g h A g s a m p l e r e -q u i r e d s p e c i a l c h e m i c a l p o l i s h i n g u s i n g as a t u r a t e d s o l u t i o n o f c h r o m i c a c i d c o n t a i n -i n g a s m a l l a m o u n t o f h y d r o c h l o r i c a c i d .T h i s s a m p l e w a s e t c h e d w i t h a w e a k s o -l u ti o n o f p o t a s s i u m d i c h r o m a t e a n d s u l-fu r i c ac id .

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Decline and Fall of the Roman Dena r ius 217

1 1 0 05 10 ~5 20

1 0 0 0

900

800

700

600

500

' t O 0

9 6 0 . 5

or(Aq) !t 4.18.8)

WEIGHT PER CENT COPPER25 30 35 40 45 50

J/ 77 9 ~ '

3 9 , 9( '281)

60 ?0 80 901o8

CtCuor (C u) -- .~..

95'92.0

3 0 0

0.35 ( 0 . 2 )2 0 0 t

0 10A q

2 0 3 0 4 0 5 0 6 0 70A T O M I C P E R C E N T C O PP ERFIG. 2. The copper-silver phase diagram.

>9994(>999}80 90 100Cu

SAVING FACE WHILE REDUCING COST

F o r a n y c o i n a g e t o c i r cu l a te f r e e l y , i t m u s tb e a c c e p t e d . T h i s i s a s u b t l e b u t r e a l e f f e c t,a s th e p r o m o t e r s o f t h e S u s a n B . A n t h o n y$ 1 c o i n d i s c o v e r e d . I f t h e s i z e , c o lo r ,w e i g h t , o r a p p e a r a n c e o f t h e c o in a re n o ta c c e p t a b l e , i t w i l l s i m p l y n o t c i r c u l a t e , a tl e a s t n o t v e r y f a r . F o r R o m e , a s f o r a n ys t a t e , i t s c o i n a g e h a d t w o a u d i e n c e s . T h ef ir s t w a s i ts c it i ze n s . T h e i r a c c e p t a n c e w a sc r it ic a l, b u t m o r e c o n t r o l l a b l e . T h e y h a d l it -t l e c h o i c e . T h i s w a s n o t t r u e f o r t r a d e b e -t w e e n n a t i o n s . L a r g e a s t h e e m p i r e w a s , i ts ti ll n e e d e d f o r e i g n a c c e p t a n c e o f i tsm o n e y . T he denarius h a d c i r c u l a t e d v e r y f ar( to I n d i a ) a n d w a s w i d e l y a c c e p t e d . I t w a si n t h e e m p e r o r ' s b e s t i n t e r e s t t o m a i n t a i nt h e a c c e p t a n c e o f t h e c o i n , h e n c e , t o m a i n -t a i n i ts a p p e a r a n c e . T h e m o r e i t l o o k e d l ik ep u r e s i l v e r, a s it s t a r t e d o u t t o b e , t h e b e t t e ri ts a c c e p t an c e . O n t h e o t h e r h a n d , t h e r ej u s t w a s n ' t e n o u g h s i lv e r t o g o a r o u n d , s o

t h e t r ic k w a s t o m a k e t h e denarius l o o k l ik ep u r e s il ve r w h e n i t w a s n o t .H e r e , t h e r u l e s o f m e t a l l u r g y f a v o r e d t h em i n t . F i r st , in t h e s o l i d s o l u t i o n r e g i o n , t h ep r e s e n c e o f c o p p e r w a s v i r tu a l ly u n n o t i c e -a b le . I t m a d e t h e c o in h a r d e r , w h i c h w a sg o o d , b u t n o t m u c h l e s s s i l v e r c o l o r e d . A ne x a m p l e o f s u c h a c o i n i s t h e d e n a r i u s o fM . T u l l i u s ( F i g . 3 ) . T h e m i c r o s t r u c t u r e o ft h i s c o i n i s i n d e e d a s i n g l e - p h a s e d s t r u c -t u r e , c o n s i s t i n g o f r e l a t i v e l y f i n e g r a i n sw i t h s o m e a n n e a l i n g t w i n s p r e s e n t. T h iss u g g e s t s t h a t f o r t h i s b l a n k , m e c h a n i c a lw o r k i n g a n d h e a t i n g p r i o r t o o r d u r i n gs t r i k i n g c a u s e d r e c r y s t a l l i z a t i o n .

T h e r e i s a d e b a t e a m o n g n u m i s m a t i s t sa b o u t h o w m u c h w o r k i n g w a s d o n e t o c oi nb l a n k s a f t e r c a s t i n g a n d b e f o r e s t r i k i n g .S o m e , a r g u i n g f r o m p r a c t i c a l e c o n o m i c s ,s a y n o n e w a s n e c e s s a r y b e c a u s e e v e n g l ob -u l a r b l a n k s c o u l d b e s t r u c k t o c o i n s i fh e a t e d . T h i s a p p e a r e d t o b e t h e c as e w i t hG r e e k c o i n a g e o f e a r l y p e r i o d s . O t h e r s ,

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2 1 8 A. W. Pense

FIc. 3. Denarius o f M . T u l l i a ; s i n g l e p h a s e ,< 9 w t . % C u , K 2 C r 2 0 2 - H 2 S O 4 e t c h .based on evidence such as that shownhere, argue that flatten ing of the blank andreheating before striking was commonRoman practice. As will be seen later, theevidence of this study is not conclusivewith respect to a standard Roman coiningpractice. Perhaps the practice was variable,dependin g on location and time.

For coins in the eutectic region of the dia-gram, other principles favorable to silvercolor in these coins applied. As might bepredicted from the phase diagram, the con-tinuous phase in the eutectic is the silver-rich one. Thus, even in the eutectic region,large amounts of copper (-30 wt.%) canbe tolerated, and the "silvery" color of thecoin is still maintained. An example of thisis a denarius of Julius Caesar, the micros-tructure of which is illustrated in Fig. 4.

This structure consists of primary Ag-richdendrites with some Cu-Ag eutectic; thecoin is abou t 14 wt. % copper. The effect ofmechanical working is not evident in thiscoin.At this point one would be inclined toask, based on Fig. 1, if this is a coin mintedprior to Augustu s, wh y is it 86 wt. % silver,not 95 wt.%? The answer illustrates an-other general trend in the decline of thedenarius. This coin was minted far fromRome. The farther from Rome, the lesslikely people are to know, care, or checkon coin fineness. In general, the decline ofthe denarius always occurred first in theprovinces. In this case, it probably wasminted by Julius Caesar in the field for histroops. So even the first Caesar felt the eco-nomic pressure of maintaining the army.From the appearance standpoint, how-ever, it was quite satisfactory, even if hedid cheat a little on its inherent value.

Similar analysis of the microstructure ofthe coin of Titus (Fig 5) shows it to be about12 wt. % copper. Once again, p rimary Ag-rich dendrites and some eutectic are pres-ent, with little effect of the coining processvisible. Actually, Titus was said to have in-creased the silver content of the denariusafter a decline under Nero, but this studydid not confirm this claim.

If we now move across time, we shouldfind little microstructural change in the de-narius for Trajan, but this proves not to beentirely true. Two coins of Trajan were

Fic. 4, Denarius of Ju l iu s C a e sa r ; - 1 4 w t . % C u , F e r r i c F xG . 5 . Denarius o f T i t u s ; - 1 2 w t . % C u , f e r r i c c h l o r i d ec h l o r i d e e t c h . e t c h ,

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Decline and Fall Of the Rom an D ena r i us 219

FIG. 6 . Denar ius of Trajan (Rome); -14wt.%, ferricchloride etch.

FIG. 8. D e n a r i u s of Faustina, --22wt. % Cu, ferric chlo-ride etch.

s t u d ie d , o n e m i n t e d in R o m e a n d t h e o t h e rin C a e s a re a i n C a p p a d o c i a . T h e R o m a nc o i n (F ig . 6) h a s a b o u t t h e e x p e c t e d c o p p e ra d d i t i o n , 1 4 w t . % , w h i l e in th e c o i n f r o mC a e s a r e a ( F ig . 7 ), i t i s m u c h g r e a t e r . T h em i c r o s t r u c t u r e c o n s i s ts o f p r i m a r y c o p p e r -r ic h p h a s e w i t h c o p p e r - s i l v e r eu t e c ti c . T h es t r u c t u r e i n d i c a t e s a n a l l o y w e l l to t h e c o p -p e r s i d e o f t h e e u t e c t i c a t a b o u t 5 0 w t . %C u . S ti ll , it l o o k e d r e a s o n a b l y g o o d a s adenar iu s .

I f w e p r o c e e d t o th e denar iu s o f F a u s t i n a ,w i f e o f A n t o n i u s P i u s , i t s h o u l d i l lu s t r a tea c o i n o f a b o u t 1 4 0 B .C .E ., a n d s h o u l d b ea b o u t 80 w t . % s il ve r , s o m e w h a t l e ss t h a nt h e e u t e c t ic . T h e m i c r o s t r u c t u r e o f t h is c o i n( Fig . 8) d e m o n s t r a t e s t h i s to b e tr u e , a l-t h o u g h t h e c o i n i n g p r o c e s s i n th i s c a se a p -

5 0 ~ , m

p e a r s t o h a v e l e ft a n a l i g n e d s t r u c t u r e w i t ht h e p r i m a r y A g - r i c h p h a s e l e s s e v i d e n t a n dt h e s i lv e r -r ic h c o n t i n u o u s p h a s e i n th e e u -t e ct ic m o r e e v i d e n t . T h i s c o i n is a ls o q u i t e" s i l v e r " in a p p e a r a n c e . T h e s i l v e r c o n t e n tis a c t u a l l y a b o u t 7 8 w t . % ( 22 w t . % C u ) .

P r o g r e s s in g w i t h t i m e , w e w o u l d n o we x p e c t t o f in d a s u b s t a n t i a l d e c r e a s e i n sil-v e r c o n t e n t . T h i s p r o v e s t o b e t r u e . S u r -p r i s i n g l y , e v e n i f w e m o v e t o a c o i n li ket h a t s e e n i n F i g . 9 , t h e denar iu s o f C a r a c a l l a( 2 1 1- 2 1 7) , w i t h a c o n t e n t o f 4 0 w t . % - 5 0w t . % c o p p e r a n d w i t h a s u b s t a n ti a la m o u n t o f p r i m a r y c o p p e r - r i c h p h a s e i nt h e m i c r o s t r u c t u r e , i t r e t a in s e n o u g h " si l-v e r ' " a p p e a r a n c e t o b e a c c e p t a b l e to m o s tp e o p l e a s a s il v e r c o i n . S o f a r s o g o o d , a sf ar a s t h e m i n t a n d t h e e m p e r o r a r e c o n -c e r n e d . T h e " c o n t i n u o u s p h a s e " w a s s til l

FIG. 7. D e n a r i u s of Trajan (Cappadocia); -50 wt. %Cu ,2% nital etch. FIG, 9. D e n a r i u s of Caracalla; 40-50wt.%Cu, ferricchloride etch.

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220 A. W. Penseworking for them, but it had about reachedits limit.The fact was, howeve r, that the mint wasincreasing the apparent wealth of the Em-pire by simply taking mon ey obtained fromtaxes or existing bullion and increasing itsquantity by addin g more copper, but verylittle silver, to the circulating coinage. Be-fore long, people knew, and inflationbegan. The inherent silver content of oldercoins began to exceed their face value, andthey were gradual ly converted to silver bycitizens as well as being converted to cheapmon ey by the mint. Thus an early exampleof Gresham's Law came into effect, i.e.,bad m one y drove the good off the market.This inflation resulted in the introduc-tion of a new coin by the emperor we callCaracalla, the A n t o n i n i a n u s , or "double de-n a r i u s " (named after himself, of course,Caracalla being his nickname, Antoninushis real one.) It was larger than the denar-ius , but weighed only about 5g (about 1denar i i ) . It had no greater fineness, andthis did little to improve things. This coin,being of equal fineness and twice thevalue, but only half again the we ight of thedenar i us , also drove the denar i us off themarket and eventually became the "silver"coin used in commerce.

The story does not end here, because theneed for coinage, and the th ings it bought ,was ever increasing. The final step was onewe have adopted even in modern times,the sandwich coin--silver on the outsideand copper on the inside. The introductionof these coins corresponds to the precipi-tous drop in the silver value of the denar i usbetween 250 and 260 c.E. The compositecoin was probably made by hot dippingblanks of low silver content in a silver chlo-ride bath before coining [7], or so it ap-pears. The microstruc ture of one such coinof Trajan Decius is seen in Fig. 10. The ex-ternal silver layer was relatively thick,probably about 0.1 ram, but corrosion hasund erm ined muc h of it, leaving a gap fromremoved corrosion product and some at-tack of the underlying core.In time, the coating became thinner and

thinner. This is exemplified by the com-posi te coin of Postumus (259-268) (Fig. 11).Here the external coating is relatively thin,a few microns. The zone between the coat-ing and the core is, once again, probablya result of corrosion. The core, surpris-ingly, is not pure copper, but has a smallamount of silver-rich phase present. Infact, there is no logical reason for this, butperhaps it represents some concession tothe fact that this was supposed to be a "sil-ver" coin, so it needed to have some silverthroughout. Even the core of the coin ofAurelian (270-275) (Fig. 12) has some silverpresent (as well as some lead). This wasapp arently official min t policy, i.e., a smallbut i ntended amount of silver was still putinto the denar i us , or A n t o n i n i a n u s .The use of "plated" or composite coinswas not new; they had been found in iso-lated examples from the provinces for sev-eral hu nd re d years before this time. We arenot sure whether they are contemporarycounterfeits or official products of mints indistressed circumstances [7], but they wererare. An example of one such denar i us issh own in Fig. 13. This was officially a de-nar i us of Augu stus , the architect of the sys-tem t hrough his edicts of 15 B.C.D. It is ob-viously not what he intended! Perhaps itis refreshing, in a way, to see that officialedicts had as much power then as they donow. This was probably a forgery, but wedo not know who profited, a clandestineentrepreneur or an unscrupulous mintmaster.

In the late 3rd Century, it was a differentstory. Now they were official and the onlycoin of the realm. The end of silver coinagewas in sight. In the next few years, the ex-ternal coating became thinner and thinneruntil it was noth ing more than a thin silverwash, like that of the coin of Postumus,rubbed off by use shortly after the coin leftthe mint. The denar i us had fallen com-pletely. One gold aureus was equal now toabout 2250 denari i . Only a major reformcould save the monetary system. Diocle-tian's Reform starting at 296 C.E. did justthis, creating a new life for silver coinage.

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Decline and F all of the Roman Denarius

J

- ~ L I:~ -$ .: [ 71 i - -

221

FIG. 10. Coin of Trajan D ecius; 2% n ital etch.C O N C L U S I O N

T h e f a l l o f t h e denar ius h a d a n u m b e r o fm o n e t a r y a n d e c o n o m i c i m p l ic a t i o n s , o n l ys o m e o f w h i c h a r e d i s c u s s e d h e r e . T h e de-nar ius r e t a i n e d i ts si ze , b u t i t w a s n o w e s -s e n t ia l l y c o p p e r . T h i s m a d e t h e l a r g e r c o p -p e r c o in s ( w h i c h n o w h a d a s m a l l e r fa c ev a l u e b u t a s i m i la r c o m p o s i t i o n a n d , t h u s ,a g r e a t e r i n t r in s i c v a l u e ) u n s t a b l e . T h e s ew e r e n o w d r i v e n o f f t h e m a r k e t . T h u s , a st h e denar ius f e ll , i t t o o k o t h e r c o i n s w i t h i t.

FIG. 12. Core of coin of Aurelian; ferric chloride etch.I t w a s a s y m p t o m o f t h e t i m e s , a r e s u l t o fc h ro n i c o v e r s p e n d i n g o f t h e b u d g e t , s o m e -t h i n g w e s t i l l d o .

T h e m i c r o s t r u c t u r e s o f t h e s e c o i n s d o t el la n i n t e r e s t i n g s to r y . H u m a n n a t u r e h a s n o tc h a n g e d t o o m u c h o v e r h i s to r y . P e o p l e s ti l ls e e k m o r e f o r l e ss , a n d h i s t o r y r e p e a t s i t -s e l f . T h e c o p p e r - s i l v e r s y s t e m s e r v e d t h ee m p e r o r w e l l b e c a u s e i t a l lo w e d a p p e a r -a n c e t o c o n c e a l fa c t. I n t h e e n d , g r e e d e x -c e e d e d c o m m o n s e n se , a n d i t b r o u g h t t h em o n e t a r y s y s t e m d o w n . T h is m a y , i n t hee n d , b e t h e m o s t u s e f u l l e s s o n w e c a n l e a rnf r o m t h i s s l i c e o f h i s t o r y .The au thor acknowledges t he spec ia l a s s i s tanceo f Ar lan Bensco te r , Research Eng ineer a t Le -h igh U nivers i t y , i n t he prepara t ion o f t he sam -pies . Wi thout h is exper t he lp , th is ar t ic le wouldnot have been poss ib le .

FIG. 11. Coin of Postum us; ferric chloride etch. FIG. 13. Plated denarius of Augustus, unetched.

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222 A . W . P e n seReferences

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c i e n t C o i n a g e , R o y a l N u m i s m a t i c S o c i e t y S p e c ia lPub l ica t ion No . 8 , Lon do n (1972) , pp . 3 -48 .7 . Cope , L . H . , Su r f ace - s i lve red anc ien t co ins , inM e t h o d s o f C h e m i c a l a n d M e t a l l u rg i c a l I n v e s t i-g a t i o n o f A n c i e n t C o i n a g e , R o y a l N u m i s m a t i cSoc ie ty Specia l Pub l ica t ion No . 8 , Lo nd on (1972),pp . 261-278 .Rece ived Ju ly 1991 , accep ted Apr i l I992 .