It seems most likey that the Achaemenids did not establish a satrapy (provincial administration) in Thrace, even though the historian Herodotus claimed that the subdued regions had to pay taxes. As a matter of fact, there is no evidence for important administrative centers. Instead, Persian authority was merely exersiced through a couple of garrisoned forts, most importantly those of Doriskos and Eion. Hence, the vast majority of Thrace remained unaffected by the Persian presence. After the failed invasion of Greece in 480-79, the Persian foothold in Europe collapsed. By around 450, Persian authority in Europe, including Thrace, had vanished entirely.