Athenians sent troops to Cyprus. Cimon defeated the Persians in the Battle of Salamis-in-Cyprus, but died of disease in 449 BC. Pericles is said to have initiated both expeditions in Egypt and Cyprus, although some researchers, such as Karl Julius Beloch, argue that the dispatch of such a great fleet conforms with the spirit of Cimon's policy. Complicating the account of this period is the issue of the Peace of Callias, which allegedly ended hostilities between the Greeks and the Persians. The very existence of the treaty is hotly disputed, and its particulars and negotiation are ambiguous. Ernst Badian believes that a peace between Athens and Persia was first ratified in 463 BC (making the Athenian interventions in Egypt and Cyprus violations of the peace), and renegotiated at the conclusion of the campaign in Cyprus, taking force again by 449–448 BC. John Fine, in contrast, suggests that the first peace between Athens and Persia was concluded in 450–449 BC, due to Pericles' calculation that ongoing conflict with Persia was undermining Athens' ability to spread its influence in Greece and the Aegean. Kagan believes that Pericles used Callias, a brother-in-law of Cimon, as a symbol of unity and employed him several times to negotiate important agreements. In the spring of 449 BC, Pericles proposed the Congress Decree, which led to a meeting ("Congress") of all Greek states to consider the question of rebuilding the temples destroyed by the Persians. The Congress failed because of Sparta's stance, but Pericles' intentions remain unclear. Some historians think that he wanted to prompt a confederation with the participation of all the Greek cities; others think he wanted to assert Athenian pre-eminence. According to the historian Terry Buckley the objective of the Congress Decree was a new mandate for the Delian League and for the collection of "phoros" (taxes). During the Second Sacred War Pericles led the Athenian army against Delphi and reinstated Phocis in its sovereign rights on the oracle. In 447 BC Pericles engaged in his most admired excursion, the expulsion of barbarians from the Thracian peninsula of Gallipoli, to establish Athenian colonists in the region. At this time, however, Athens was seriously challenged by a number of revolts among its subjects. In 447 BC the oligarchs of Thebes conspired against the democratic faction. The Athenians demanded their immediate surrender, but after the Battle of Coronea, Pericles was forced to concede the loss of