in historical sources. In 615, during the reign of Heraclius (r. 610–641), the whole Balkans was regarded as Sklavinia – inhabited or controlled by Slavs. Chatzon led the Slavic attack on Thessaloniki that year. The Slavs asked the Avars for aid, resulting in an unsuccessful siege (617). In 626, Sassanids, Avars and Slavs joined forces and unsuccessfully besieged Constantinople. During the same year of the siege, the Sclaveni used their monoxyla in order to transport the 3,000 troops of the allied Sassanids across the Bosphorus which the latter had promised the khagan of the Avars. In 630, Sclaveni attempted to take Thessaloniki again. Traditional historiography, based on the De Administrando Imperio, holds that the migration of Croats and Serbs to the Balkans was part of a second Slavic wave, placed during Heraclius' reign. Constans II conquered Sklavinia in 657–658, "capturing many and subduing", and settled captured Slavs in Asia Minor; in 664–65, 5,000 of these joined Abdulreman ibn Khalid. Perbundos, the chieftain of the Rhynchinoi, a powerful tribe near Thessaloniki, planned a siege on Thessaloniki but was imprisoned and eventually executed after escaping prison; the Rhynchinoi, Strymonitai and Sagoudatai made common cause, rose up and laid siege to Thessaloniki for two years (676–678). Justinian II (r. 685–695) settled as many as 30,000 Slavs from Thrace in Asia Minor, in an attempt to boost military strength. Most of them however, with their leader Neboulos, deserted to the Arabs at the Battle of Sebastopolis in 692. 8th century Military campaigns in northern Greece in 758 under Constantine V (r. 741–775) prompted a relocation of Slavs under Bulgar aggression; again in 783. The Bulgars had by 773 cut off the communication route, the Vardar valley, between Serbia and the Byzantines. The Bulgars were defeated in 774, after Emperor Constantine V (r. 741–775) learnt of their planned raid. In 783, a large Slavic uprising took place in the Byzantine Empire, stretching from Macedonia to the Peloponnese, which was subsequently quelled by Byzantine patrikios Staurakios (fl. 781–800). Dalmatia, inhabited by Slavs in the interior, at this time, had firm relations with Byzantium. In 799, Akameros, a Slavic archon, participated in the conspiracy against Empress Irene of Athens. Relationship with Byzantium Byzantine literary accounts (such as John of Ephesus) mention Slavs raiding areas of Greece in the 580s. According to later sources such as The Miracles of Saint Demetrius, the Drougoubitai, Sagoudatai, Belegezitai, Baiounetai, and Berzetai