or Aurelius Ambrosius, a famous general of the ancient Britons, of Roman extraction. He was educated at the court of Aldroen of Armorica, who, at the request of the Britons, sent him over with 10,000 men to assist them against the Saxons, whom Vortigern had invited into Britain. Ambrosius was so successful against the Saxons, that the Britons chose him for their king, and compelled Vortigern to surrender to him all the western part of the kingdom, divided by the Roman highway now called Watling Street. Some time after, the Britons being discontented with Vortigern, and having withdrawn their allegiance from him, he retired to a castle in Wales. Here, being besieged by Ambrosius, and the castle taking fire, he perished in the flames, and left his rival sole monarch of Britain, who now assumed the imperial purple, after the manner of the Roman emperors. Geoffrey of Monmouth tells us that Ambrosius built Stonehenge, near Salisbury, in Wiltshire. See STONEHENGE.

After the Britons had defeated the Saxons, and obliged them to retire northward, Ambrosius is said to have convened the princes and great men at York, where he gave orders for repairing the churches destroyed by the Saxons, and restoring the exercise of religion to its former lustre. "He was a man," says Geoffrey, "of such bravery and courage, that when he was in Gaul no one durst enter the lists with him; for he was sure to unhorse his antagonist, or to break his spear into shivers. He was, moreover, generous in bestowing, careful in performing religious duties, moderate in all things, and more especially abhorred a lie. He was strong on foot, stronger on horseback, and perfectly qualified to command an army." The same author tells us that he was poisoned at Winchester, by one Eopa, a Saxon disguised as a physician, and hired for that purpose by Pascentius, one of the sons of Vortigern; but the generally received opinion is, that he was killed in a battle which he lost in the year 508, against Ceretic, one of the Saxon generals.