The attacks of the Slavs and of the newly-founded Arabian power marked the course of the seventh century. In 623 the Slavs made an incursion into Crete, and that island, of which we have heard little under the Imperial rule, was also visited by the Arabs in 651 and 674. But though the Cretans were forced to pay tribute to the Caliph, Moawyah, they were treated with kindness by the politic conqueror. About the same time as this second Arab invasion, and while the main Arab force was besieging Constantinople, a body of Slavs seized the opportunity to settle in the rich plain of Thessaly, and it is from one of their tribes that the present town of Velestino, so often mentioned in the war of 1897, received its name. Yet this tribe soon became so friendly that it assisted the Greeks in the defence of Salonika against a Slavonic army—a further proof of the readiness with which the Slavs adopted the Greek point of view. It is clear also that the command of the Imperial troops in Greece was regarded as an important post, for we find it entrusted to Leontios, who made himself Emperor. The Greek islands were still used as places of detention for prisoners of position. Thus Naxos was chosen as the temporary exile of Pope Martin I by the Emperor Constans II, and the future Emperor Philippicus was banished to Cephalonia. A new era opened for the Empire with the accession of Leo the Isaurian in 716. In the first place, that sovereign completed the reform of the system of provincial administration, which had lasted more or less continuously since the time of Constantine. In place of the old provincial divisions, the Empire was now parcelled out into military districts, called Themes—a name originally applied to a regiment and then to the place at which the regiment was quartered. The choice of such a title indicates the essentially military character of the new arrangement, which implied the maintenance of a small division of troops in each district as a necessary defence against the Avars, Slavs, and Arabs, whose depredations had menaced provinces seldom exposed to attack in the old times. Six out of the twenty-eight Themes comprised Greece, as she was before the late Balkan wars. The Peloponnese, with its capital of Corinth, formed one; Central Greece, including Eubœa, formed another, under the name of Hellas, but its capital was Thebes, not Athens; Nikopolis, which comprised Ætolia and Akarnania, and Cephalonia (the latter created a separate Theme later on, and including all the Ionian Islands) were two more; the Ægean Sea, popularly known as the Dodekannesos, or “twelve islands,” composed one of the Asian Themes, and Thessaly was a part of the Theme of Macedonia. Both the military and civil authority in each Theme was vested in the hands of a Commander, known as _strategós_, except in the case of the Ægean Islands, where the post was filled by an Admiral, called _droungários_. Under the