This paper reexamines the long-standing problem of the nature and magnitude of the catastrophic Hellenic expedition to Egypt c. 460-454. An uneasy scholarly consensus posits that many fewer than the 200 triremes implied by Thucydides were involved in the momentous defeat, yet the arguments employed by proponents and detractors of this hypothesis have not been decisive. This paper attempts to develop a better understanding of the final stages of the campaign in order to settle the question of losses. Thucydides offers the most reliable narrative of the events in Egypt (1.104, 109-10), but the compressed nature of the pentekontaetia has left us with a brief, lacunary text. Examination of the verbs poliorkein and kataklēiein and the noun poliorkia in appropriate contexts throughout Thucydides' history reveals that the words connote a tight blockade that seeks to deny all supplies to the besieged; the terms do not normally convey less stringent varieties of military harassment. Application of this understanding to the passages in question shows that the 200 triremes initially mentioned by Thucydides could not possibly have been engaged in Egypt when the siege of Prosopitis island began: a force of such size under a tight blockade could never have held out for 18 months. This conclusion is supported by an economic and demographic survey of the fifth-century B.C. Egyptian Delta, which suggests that resources would not have been plentiful in the region. A much smaller Greek force, perhaps 40 to 50 triremes, must have been involved in the final siege.