Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Caesar does not seem any more than the earlier government to have contemplated the regulation with a view to unity of the monetary system of the east, where great masses of coarse silver money--much of which too easily admitted of being debased or worn away--and to some extent even, as in Egypt, a copper coinage akin to our paper money were in circulation, and the Syrian commercial cities would have felt very severely the want of their previous national coinage corresponding to the Mesopotamian currency.
We find here subsequently the arrangement that the -denarius- has everywhere legal currency and is the only medium of official reckoning,(115) while the local coins have legal currency within their limited range but according to a tariff unfavourable for them as compared with the -denarius-.(116)
115. There is probably no inscription of the Imperial period, which specifies sums of money otherwise than in Roman coin.
116. Thus the Attic -drachma-, although sensibly heavier than the -denarius-, was yet reckoned equal to it; the -tetradrachmon- of Antioch, weighing on an average 15 grammes of silver, was made equal to 3 Roman -denarii-, which only weigh about 12 grammes; the -cistophorus- of Asia Minor was according to the value of silver above 3, according to the legal tariff =2 1/2 -denarii-; the Rhodian half -drachma- according to the value of silver=3/4, according to the legal tariff = 5/8 of a -denarius-, and so on.
This was probably not introduced all at once, and in part perhaps may have preceded Caesar; but it was at any rate the essential complement of the Caesarian arrangement as to the imperial coinage, whose new gold piece found its immediate model in the almost equally heavy coin of Alexander and was doubtless calculated especially for circulation in the east.
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Reference address : https://www.ellopos.net/elpenor/rome/5-11-old-republic-new-monarchy.asp?pg=177