Having effected this, the Emperor Justinian, learning that all the cities in Peloponnesus were unwalled, and reflecting that much time would be wasted if he attended to the security of each one, securely fortified the whole isthmus with a wall, since the existing wall was mostly in ruins. Upon this wall he built forts and established garrisons in them, and in this manner rendered the whole country of Peloponnesus safe from the enemy, even though any misfortune should befall the fortifications at Thermopylæ. III. Diocletianopolis in Thessaly was in ancient times a flourishing city, but latterly was ruined by the incursions of the barbarians, and had long been without inhabitants. There is a lake near it, which is called Castoria, in the midst of which is an island surrounded by water, with only one narrow passage, not wider than fifteen feet, leading to it through the lake. On this island stands a very lofty mountain, which overhangs the lake on one side and the island on the other; wherefore our Emperor decided against the site of Diocletianopolis, because it was obviously exposed to attack, and had long before suffered the misfortunes which I had mentioned, but built a very strong city on the island, to which he naturally gave his own name. Besides this, he removed the walls of Echinæum, Thebes, Pharsalus, and all the other cities of Thessaly, amongst which are Demetrias, Metropolis, Gomphi, and Tricattus, and securely fortified them, for their walls were decayed by age and could easily be taken by an enemy. Now that we have come to Thessaly, let us proceed to Mount Pelion and the river Peneus. The Peneus flows in a gentle stream past Mount Pelion, and in its course adorns the city of Larissa, for Phthia no longer exists, but has perished through age. The river flows with a quiet stream as far as the sea, and the neighbouring country is rich in fruits of all kinds, and in sweet waters, which the inhabitants were never able to enjoy, as they were in continual expectation of an attack from the barbarians; for there was no strong place anywhere in these regions to which they could fly for refuge, but the walls of Larissa and Cæsarea were so ruinous that they were almost open towns. The Emperor Justinian, by rebuilding the walls of both these cities very strongly, enabled the country to enjoy true prosperity. Not far from hence rise precipitous mountains covered with lofty trees. These mountains were the home of the Centaurs; and in this country the battle of the Centaurs with the Lapithæ took place, as the ancient myths declare, which inform us that in old times there dwelt there a monstrous race combining the forms of two creatures. Antiquity gives some warrant for this fable by the name of a fort in these mountains, which down to my own time was named Centauropolis, whose ruinous walls the Emperor Justinian restored and strengthened, together with those of Eurymene in the same country, which had fallen into the same condition.