In 1446 Constantine Palaiologos, then Despot of the Morea, sent George on a diplomatic mission to Murad II to obtain the independence of the Greek states south of Thermopylae; enraged at the offered terms, the Sultan put George Chalkokondyles into prison, then marched on Constantine's forces holding the Hexamilion wall on the Isthmus of Corinth and after bombarding it for three days, destroyed the fortifications, massacred the defenders, then pillaged the countryside, ending all hopes of independence.