After seizing Cyprus in 649 and raiding Rhodes, Crete and Sicily, the young Arab navy decisively defeated the Byzantines under the personal command of Emperor Constans II (641–668) in the Battle of the Masts of 655. This catastrophic Byzantine defeat opened up the Mediterranean to the Arabs and began a centuries-long series of naval conflicts over the control of the Mediterranean waterways. From the reign of Muawiyah I (661–680), raids intensified, as preparations were made for a great assault on Constantinople itself. In the long first Arab siege of Constantinople, the Byzantine fleet proved instrumental to the survival of the Empire: the Arab fleets were defeated through the use of its newly developed secret weapon, "Greek fire". The Muslim advance in Asia Minor and the Aegean was halted, and an agreement to a thirty-year truce concluded soon after.