From Project Athinai
The Argyrokopeion (mint) was built somewhere between 430 and 404 BC at the south-east corner of the Agora. Therefore, it is possible that it already existed during our period of reference (421 BC).
The building consisted of several rooms of various sizes grouped around a courtyard.
This is where the Attic currency, the drachma, was manufactured. The one drachma silver coin weighted 4,36 gr. There were also 2 drachmas (didrachma), four drachmas (tetradrachma) and ten drachmas (dekadrachma) coins. The drachma was subdivided into six oboloi also made of silver. There were one, two and three oboloi coins.
All Athenian coins featured a helmeted profile bust of Athena on the obverse (front) and an owl, a crescent, an olive sprig and the three first letters of the name of the city on the reverse (back). These coins were commonly referred to as the "Owls of the Laurion".
American School of Classical Studies at Athens; The Athenian Agora: A Guide to the Excavation and Museum, 1990
Flacelière, Robert, La vie quotidienne en Grèce au siècle de Périclès, Hachette, 1959, p. 151