that the Spartans' inability to attack and control Megara was due to poor calculations and Athenian efforts to avoid an open land battle with the Spartans. Athenian crisis and the truce Athens' remarkable string of successes came to a sudden halt in 454 BC, when its Egyptian expedition was finally crushingly defeated. A massive Persian army under Megabazus had been sent overland against the rebels in Egypt some time earlier, and upon its arrival had quickly routed the rebel forces. The Greek contingent had been besieged on the island of Prosopitis in the Nile. In 454 BC, after a siege of 18 months, the Persians captured the island, destroying the force almost entirely. Though the force that was obliterated was probably not as large as the 200 ships that had originally been sent, it was at least 40 ships with their full complements, a significant number of men. It was in 454 that the treasury of the Delian League, which Athens was head of, was moved from Delos to Athens. This change gave Athens greater control over the finances of the league, and a number of inscriptions survive showing who contributed to the wealth of the league and how much each city gave. Osborne and Rhodes' new book containing a great number of the inscriptions available from this period has one tribute list from 454/3 depicting the amount of tribute which Athens received from its allies and which it dedicated to Athena. The change in the location of the treasury is often pin-pointed as a focal point for the realisation of an Athenian empire. The disaster in Egypt severely shook Athenian control of the Aegean, and for some years afterwards the Athenians concentrated their attention on reorganising the Delian League and stabilising the region. The Athenians responded to a call for assistance from Orestes, the son of Echecratides, King of Thessaly, to restore him after he was exiled. Together with their Boeotian and Phocian allies, the Athenians marched to Pharsalus, today's Farsala. They were not able to achieve their goals because of the Thessalian cavalry and were forced to return to Athens not having restored Orestes or captured Pharsalus. Therefore, in 451 BC, when Cimon returned to the city, his ostracism over, the Athenians were willing to have him negotiate a truce with Sparta. Cimon arranged a five-year truce, and over the next several years Athens concentrated its efforts in