unless they were burned, or the ground undermined upon which they stood, except by overturning them with stones or iron-shod beams hung from a mast on the wall, or by increasing the height of the wall, or the erection of temporary towers on the wall beside them. [Sidenote: The advantages of defenders.] [Sidenote: Ordinary way of capture.] [Sidenote: Strength and advantage of fortresses.] Thus there was no ancient fortification capable of withstanding a long siege when the besieged city was, short of defenders or provisions. With equal forces an attack was generally a failure, for the defenders had always a great advantage. But when the number of defenders was reduced, or when famine pressed, the skill and courage of the assailants would ultimately triumph. Some ancient cities made a most obstinate resistance, like Tarentum; Carthage, which stood a siege of four years; Numantia in Spain, and Jerusalem. When cities were of immense size, population, and resources, like Rome when besieged by Alaric, it was easier to take them by cutting off all ingress and egress, so as to produce famine. Tyre was only taken by Alexander by cutting off the harbor. Babylon could not have been taken by Cyrus by assault, since the walls were three hundred and thirty-seven feet high, according to Herodotus, and the ditch too wide for the use of battering-rams. He resorted to an expedient of which the blinded inhabitants of that doomed city never dreamed, which rendered their impregnable fortifications useless. Nor would the Romans have probably prevailed against Jerusalem had not famine decimated and weakened the people. Fortified cities, though scarcely ever impregnable, were yet more in use in ancient than modern times, and greatly delayed the operations of advancing armies. And it was probably the fortified camp of the Romans, which protected an army against surprises and other misfortunes, which gave such efficacy to the legions. [Sidenote: The Tribunes.] [Sidenote: The Centurions.] [Sidenote: Gradation of ranks.]