Byzantium was conquered by a Persian general of Darius, and for a time was nothing but a Persian fortress: the Greek inhabitants of the place then dispersed, but the whole of the Bosporus and the country on the other side of the Ceras as far as Selymbria, consisted of Byzantian προάστεια. The circumference of the ancient city was not great, occupying only about double the space of the present Seraglio. During the Macedonian period, Byzantium, with extraordinary skill, preserved its independence. In Olymp. 106, it undertook, in conjunction with Rhodes, Chios, and Mitylene, the Social war against Athens. Under Lysimachus, it appears to have formally maintained its political existence, paying homage to him only by presents, and thus throughout all changes it remained free until the time of the Romans. In the age of Cicero, for example, Byzantium, as we see from his speech against Piso, was a completely free city and in alliance with the Romans. As commerce was constantly increasing in the Roman empire, Byzantium also rose in prosperity, as is clear from certain statements of Tacitus. In the war of Pescennius Niger against Septimius Severus, Byzantium stood out against a desperate siege which lasted for three years; Niger had no hope of conquering Severus and the West, and this seems to have suggested to him the idea of dividing the empire, and of maintaining himself in the East, of which Byzantium was to be the capital. When the city was taken, Severus destroyed it completely, a piece of revenge which was otherwise opposed to the character of that prudent emperor. The unfortunate consequence was, that those seas were now thrown open to the barbarians. The Goths, without any obstacle, penetrated into the Propontis, overpowered the _claustra_ of the Hellespont, and spread over Greece. At length Constantine restored Byzantium under the name of Constantinople; he saw the necessity of founding a strong capital there, if he was to maintain himself in the East. This determination of Constantine has been censured, and the course of events seems to justify the censure; but people overlook the fact that, if Constantine had not acted as he did, the East would have been conquered first and much earlier, that part of the empire being then much more in danger than the West. The Goths were on the Danube, and the Huns were pressing on from the East, while the Germans had been completely overpowered by the victories of Aurelian and Probus; and in Gaul, too, not a man thought of making war against Rome. The fact that afterwards circumstances turned out differently is no proof that Constantine was wrong. Had not Constantinople been so strong a place at that time, the eastern empire would have been lost. The gradual extension of Constantinople is a subject which would lead me too far; but if, after I have given you the topography of Rome, there he still time left, I shall add that of Constantinople.