The siglos was the Achaemenid Persian silver coin used alongside the gold daric.
The siglos formed the principal silver denomination of the Achaemenid monetary system. Its name comes through Greek usage and is related to an older Near Eastern weight term. The coin typically carried the royal archer design also seen on many darics.
Darics and siglos were not identical: the daric was gold, while the siglos was silver. Their relationship helped Persian authorities make payments and account for value across an empire that stretched from Anatolia to Central Asia and Egypt.
A siglos is sometimes described as a Persian “shekel,” because its weight reflects Near Eastern monetary traditions. However, the standard Achaemenid coin name is siglos. Coins varied somewhat in weight and wear, so surviving specimens are studied by type as well as denomination.