I like these coins, though I only have a few. There's no more archaic-looking silver coin available for such a reasonable price. Banker's marks and other interesting countermarks are common.
ANS Notes and Monographs No. 136, Two Hoards of Persian Sigloi, by Sydney P. Noe, documents two lots of these coins, of uncertain provenance, that came on the New York market in 1950. #63 shows a countermark similar to this remarkable calf's head behind the Great King's elbow, but facing right rather than left. #14 and 15 appear to be from the same punch die as this coin.
10/2004: Just stumbled across some pictures of coins of Kolchis and noticed the similarity to the bull reverses of those coins. Interesting.
Information on the AchaemenidsComments and corrections