At what period the Romans substituted a wall of defence in place of the old earthworks is uncertain, but previous to its construction they appeared to have erected two forts on the north bank of the Thames—one at the eastern extremity of the City, where the tower now stands; the other at the western end, where the Fleet fell into the Thames. That it was an open town, or very imperfectly defended, in the middle of the first century, is evidenced by the facility with which Queen Boadicea, _temp._ Nero, entered it with her army, slaughtered the inhabitants, and most probably burnt it, as the charred remains of a great conflagration have been frequently found in making deep excavations. Henry of Huntingdon, and some other of the old chroniclers, tell us that it was first walled by Constantine the Great, at the request of his mother Helena, and that the materials he made use of were hewn stone and British bricks, and that it was in compass about three miles. Camden seems to credit this statement, from the fact that coins of the Empress Helena have been found under the wall, but as these might have been in circulation long after her death, it only goes to prove that the wall was not built before her era. Constantine died in the year 337, and we find some twenty-five years afterwards London was entered and pillaged, and the inhabitants reduced to a state of great misery, by a combined army of Picts, Scots, Saxons, and Franks, which would scarcely have been possible if it had been walled, and defended by the disciplined soldiers of the empire. The probability seems to be that the walls were either built or commenced by Theodosius, the Roman general, afterwards emperor, who in the reign of Valentinian, came to Britain with an army, utterly routed the pirates and freebooters, and entered London in triumph, where he remained for a considerable period; and we are told by Ammianus Marcellinus that before he left the island he restored to their ancient sound condition both the towns and military strongholds throughout the country, and put everything in such a state of defence that peace was maintained until the reign of Honorius, when Britain was abandoned by the Romans. Hence we may arrive at an approximate date for the building of the walls. Constantine came to the throne in 306, and Valentinian died 375: and it is almost certain that it took place some time within these 70 years, the balance of evidence seeming to refer it farther to the period of the sojourn of Theodosius in Britain, or about 368-70.