betraying no flaws and easy to guard.  Many large towers occupied an exposed position outside it, with windows set close together on every side so that those assaulting the fortification in a circle would be cut off between them.  Being built at a short distance from the wall and not in a regular line, but one here and another there over a rather crooked route, they were sure to command both sides of any attacking party.  Of the entire circuit the part on the land side reached a great height so as to repel any who came that way:  the portion next to the sea was lower.  There, the rocks on which it had been reared and the dangerous character of the Bosporus were effective allies.  The harbors within the wall had both been closed with chains and their breakwaters carried towers projecting far out on each side, making approach impossible for the enemy.  And, in fine, the Bosporus was of the greatest aid to the citizens.  It was quite inevitable that once any person became entangled in its current he should willy-nilly be cast up on the land.  This was a feature quite satisfactory to friends, but impossible for foes to deal with.

[Sidenote:—­11—­] It was thus that Byzantium had been fortified.  The engines, besides, the whole length of the wall, were of the most varied description.  In one place they threw rocks and wooden beams upon parties approaching and in another they discharged stones and missiles and spears against such as stood at a distance.  Hence over a considerable extent of territory no one could draw near them without danger.  Still others had hooks, which they would let down suddenly and shortly after draw up boats and machines.  Priscus, a fellow-citizen of mine, had designed most of them, and this fact both caused him to incur the death penalty and saved his life.  For Severus, on learning his proficiency, prevented his being executed.  Subsequently he employed him on various missions, among others at the siege of Hatra, and his contrivances were the only ones not burned by the barbarians.  He also furnished the Byzantines with five hundred boats, mostly of one bank, but some of two banks, and equipped with beaks.  A few of them were provided with rudders at both ends, stern and prow, and had a double quota of pilots and sailors in order that they might both attack and retire without turning around and damage their opponents while sailing back as well as while sailing forward.

[Sidenote:—­12—­] Many, therefore, were the exploits and sufferings of the Byzantines, since for the entire space of three years they were besieged by the armaments of practically the whole world.  A few of their experiences will be mentioned that seem almost marvelous.  They captured, by making an opportune attack, some boats that sailed by and captured also some of the triremes that were in their opponents’ roadstead.  This they did by having divers cut their anchors under water, after which they drove nails into the ship’s bottom and with cords attached thereto and running from friendly territory they would draw the vessel towards them.  Hence one might see the ships approaching shore by themselves, with no oarsman nor wind to urge them forward.  There were cases in which merchants purposely allowed themselves to be captured by the Byzantines, though pretending unwillingness, and after selling their wares for a huge price made their escape by sea.