Precious (Noble) Metal Weight Standards
Ancient Greek, Roman, and Byzantine

Before coins were ever stuck, and even thereafter for many centiries, the ordinary person primarily transacted purchases by means of barter. The earlier coins were mainly used by governments (public works, mercenary armies, etc) and merchants (foreign trade) to facilitate ease of transactions.

The silver drachm of the Greek Hellenistic period represented two days wages for a soldier, and a tetradrachm therefore eight days pay. The rough equivalent today would have the tetradrachm worth approximately USD 800. It is therefore obvious that the drachm and tetradrachm were not used by the ordinary person in small transactions since they represent a huge sum of money.

The coinage was found particularly useful by merchants and traders. A ship's captain need not attempt to find a suitable cargo in barter any longer since the silver tetradrachm was universally accepted at any port. It was common to stack the tetradrachmae in groups of ten coins, tied together by twine. Since these coins did not actually circulate for ordinary purchases, it is not surprising a great many are extant today in excellent condition.

The use of bullion bars of metal in trade predates coinage. These bars were made to be of equal weight, and were called Talents. Many different standards or weights for the talents were used over time. For the sake of brevity, the Greek talent of the post-Hellenistic age and the Roman talent are related below, along with their fractions, and how any particular coinage relates to the talent.

Greek

Talent = c. 26.17kg
60 Mine = 1 Talent
1 Mine = 436.224g
100 drachmae = 1 Mine
6000 drachmae = 1 Talent
1 drachm = 4.36g
1 tetradrachm = 4 drachmae = 17.45g
25 tetradrachmae = 1 Mine
1500 tetradrachmae = 1 Talent

Roman

Talent = c. 32.71 kg
100 libra = 1 Talent (a libra is commonly called a Roman pound)
1 libra = exactly ¾ Greek Mine
1 libra = 327.168g
1 aureus = 1/44 libra = 7.44g (Note 1)
1 solidus = 1/72 libra = 4.54g (Note 2)
1 drachma = 1/96 libra = 3.41g
1 siliqua = 1/1728 libra = 0.189g

Note1: Aureus struck 44 to the pound to the time of Septimius Severus. Previously struck at 40, 42, and 43 to the pound (40 to the pound equalled c. 8.18 grams, similar to the gold stater of Greek Macedon. The aureus was continually devalued (in weight, not gold content) for some time until eventually the solidus became the gold standard.
Note 2: The solidus was always struck at 72 to the pound from the Roman through the Byzantine period - approximately 650 years. No coinage before or since was struck to the same standard of weight and purity for such an extended time.