34 Chrissis
swiftly defeated Manfred and assumed control of the Sicilian Regno, Charles
soon turned his attention eastwards to Constantinople and the Morea. The
turning point was the signing of the Viterbo Treaties, in May 1267. With these
two documents, the first between Charles and Baldwin ii, and the second
between Charles and Prince William ii of Achaea, Angevin overlordship or
direct control over the greatest part of Latin Romania was recognised.25 From
this point on, Charles was effectively placed at the head of any crusading activ-
ity in Greece. In the treaties, he had committed himself to launching, at his
own expense and with his own forces, a considerable expedition to reclaim
Constantinople. Charles was a determined and exceptionally capable ruler and
his ambitions might have even extended to the imperial throne of Byzantium.
For a time he seemed unstoppable and the immense threat he posed became
the main concern of Byzantine foreign policy. However, a number of factors
frustrated his efforts, including Venice’s aloofness towards Angevin involve-
ment in its sphere of influence. Most importantly, the Byzantine emperor,
Michael viii Palaiologos, used all his diplomatic skill to undermine Charles by
approaching the papacy and offering the prospect of Church Union as a way of
de-legitimising a crusade attack on the empire. Pope Gregory x (1271–76) was
particularly well-disposed to that prospect, and the contact between the two
sides culminated in the proclamation of the Union of the Greek and Roman
Churches at the Second Council of Lyon in 1274. This effectively cancelled out
the possibility of a crusade against Byzantium and was a serious setback for
Charles’s plans, made worse by the defeat of his expeditionary force at Berat
in spring 1281.26 A new opportunity presented itself with the elevation of the
pro-Angevin Martin iv on the papal throne, followed by the annulment of
Church Union and the excommunication of Michael Palaiologos (November
1281).27 But just as Charles of Anjou seemed ready to launch his long-awaited
campaign in Greece, the major uprising of the Sicilian Vespers brought about
the collapse of Angevin control over the island.28 The Sicilian Vespers, which
were caused by the harsh treatment of the native population, but which were
also organised with the involvement of King Peter iii of Aragon and of Michael
25 Hendrickx, “Régestes, ” pp. 184–85, nos. 300–01; Setton, Papacy, 1:103–05.
26 Deno J. Geanakoplos, Emperor Michael Palaeologus and the West, 1258–1282: A Study in
Late Byzantine-Western Relations (Cambridge, Mass., 1959); Joseph Gill, Byzantium and the
Papacy, 1198–1400 (New Brunswick, 1979), pp. 113–81; Burkhard Roberg, Das zweite Konzil
von Lyon (1274) (Paderborn, 1990), pp. 59–87, 219–81.
27 Ferdinand M. Delorme and Aloysius L. Tautu, eds., Acta Romanorum Pontificum ab
Innocentio v ad Benedictum xi (1276–1304), pc/cico (Vatican, 1954), no. 53; Gill, Papacy,
pp. 178–79.
28 Steven Runciman, The Sicilian Vespers: A History of the Mediterranean World in the Later
Thirteenth Century (Cambridge, 1958).