Where the British leader was stationed it is hard to say. The course of the Thames, meandering among marshes, must have varied much from what it is to-day, and, having no embankments, it was probably much shallower. Cæsar may have crossed near Brentford or Halliford; there are said to be the remains of a stockade in the bed of the river opposite the former place. At any rate, Cæsar gives the impression that the ford was well known. Its northern end was guarded by entrenchments, and the passage itself was obstructed by stakes. The position was a formidable one, yet it was carried with unexpected ease. The Roman cavalry led the way into the Thames, the infantry followed, with the water at their necks, passed the stakes--how we do not know--carried the stockade, and drove the Britons off towards the north. [Illustration: CÆSAR’S TWO EXPEDITIONS TO BRITAIN IN 55 AND 54 B.C. The probable line of advance on Verulam is indicated by the broken line.] Cæsar, having passed the Thames, halted for a time to receive hostages and supplies from the neighbouring Trinobantes. Caswallon fell back on his tribal stronghold (almost certainly Verulam), and sent orders to the four sub-kings of Kent to attack Cæsar’s base-camp, and so draw him back from the Thames. It was the last fine stroke of Caswallon’s admirable strategy, but fate was against him. Atrius marched boldly out to attack the men of Kent, defeated and scattered them with great loss, capturing a prominent chief named Lugotorix. Cæsar, having rested his men in the Trinobantian territory near London, advanced upon Verulam. He describes it as a great earthwork among woods and marshes. It was captured by a simultaneous attack on two fronts. The British loss was heavy, and included thousands of captives, besides vast quantities of supplies. Verulam had evidently been the place of refuge of a great part of the tribe.