especially in Cilicia, were gradually abandoned. The success of these raids emboldened the Arabs, who prepared for a second assault against Constantinople as early as the reign of Caliph al-Walid I (). After his death, his successor, Sulayman () continued planning the campaign, Sulayman began assembling his forces in late 716, on the plain of Dabiq, north of Aleppo, entrusting the command of these forces to his brother, Maslama ibn Abd al-Malik. The Slavs and Bulgars also formed a growing threat to the northern frontier of the Byzantine Empire, threatening Byzantine control in the Balkans. During the rule of Byzantine Emperor Philippicus (), in 712, the Bulgarians under Khan Tervel advanced as far as the walls of Constantinople itself, plundering the surrounding country, including villas and estates near the capital, where the Byzantine elites often summered. Theodosius came to power during a period called the Twenty Years' Anarchy, defined by struggles between the emperors and the elites, and political instability, with a rapid succession of emperors. The nobles of this time were often natives of Asia Minor, and rarely had a strong agenda beyond preventing the emperors from growing stronger and disrupting the status quo. The Twenty Years' Anarchy began when Emperor Justinian II was overthrown by Leontius () in 695, ending the Heraclian dynasty, which had retained power for eighty years. During this period of anarchy, seven different emperors took the throne, including a restored Justinian for a time. The modern historian Romilly Jenkins states that between 695 and 717 the only competent emperors were Tiberius III () and Anastasius II (). The crisis was ended by Emperor Leo III (), who overthrew Theodosius, and whose dynasty reigned for 85 years. Rise to the throne Sulayman's preparations, including his construction of a war fleet, were quickly noticed by the Byzantine Empire. Emperor Anastasius II began making preparations to defend against this new onslaught. This included sending the patrician and urban prefect, Daniel of Sinope, to spy on the Arabs, under the pretense of a diplomatic embassy, as well as shoring up the defences of Constantinople, and strengthening the Byzantine navy. The 9th-century Byzantine historian Theophanes states that in early 715 Anastasius II had commanded the navy to gather at Rhodes to then advance to Phoenix. It was there that the troops of the Opsician Theme mutinied against their commander, John the Deacon, killing him before sailing for Adramyttium, in