A period of Byzantine supremacy at sea followed the failed sieges of Constantinople and the virtual disappearance of the Muslim navies, until the re-commencement of Muslim raiding activity towards the end of the 8th century, both by the Abbasid fleets in the East as well as by the new Aghlabid dynasty in Ifriqiya.[6] Then, in the 820s, two events occurred that shattered the existing balance of power and gave the Muslims the upper hand. The first was the capture of Crete by a band of Andalusian exiles (c. 824/827) and the establishment of a piratical emirate there, which withstood repeated Byzantine attempts to reconquer the island. This opened up the Aegean Sea to Muslim raids and put the Byzantines on the defensive.