When Hengist saw that a suitable moment had come for his act of treachery, he bellowed out: Nimet our saxes! He himself immediately seized hold of Vortigern and held him tight by his royal robe. The moment they heard this signal the Saxons drew their daggers, attacked the leaders standing near them and cut the throats of about four hundred and sixty counts and earls, who were thinking of something quite different. Afterwards the holy Eldadus buried the corpses and said the last rites over them according to the custom of the Christian Church: this not far from Kaercaradduc, which is now called Salisbury, in the cemetery beside the Cloister of Ambrius, who had founded it there himself many years before. [VI.15]

AMESBURY appears in Geoffrey as Mount Ambrius and the cloister of Ambrius. Tatlock notes that the contemporary version of the name was Ambresburia, and suggests that Geoffrey’s abbot Ambrius, founder of the cloister, is derived from that name (p. 39). Ambrius is named as the founder again in Geoffrey's account of Aurelius's decision to erect a monument to the victims of the massacre:

Next he went to Winchester, to restore that town as he had restored others like it. As soon as he had repaired everything that needed such attention if the town was to be restored at all, he took the advice of Bishop Eldadus and visited the monastery near Kaercaradduc, which is now called Salisbury. It was there that were buried the leaders and princes whom the infamous Hengist had betrayed. A monastery of three hundred brethren stood there, on Mount Ambrius, for it was Ambrius, so they say, who had founded the monastery years before. As Aurelius inspected the place in which the dead lay, he was moved to compassion and burst into tears. In the end he turned his mind to other considerations, asking himself what he could do to ensure that the spot should be remembered; for it was his opinion that the greensward covering so many noble men who had died for their fatherland was certainly worthy of some memorial. [VIII.9]

The monument Aurelius erects is the Giants’ Ring: see STONEHENGE on the map for more detail. Later, both Aurelius and his brother Uther Pendragon are buried there:

After this great undertaking, Uther set out for Winchester with all possible speed. Messengers who came to meet him told him of the King’s death, saying that Aurelius was soon to be buried by the bishops of the country near the monastery of Ambrius and inside the Giants’ Ring. [VIII.16]

As soon as the death of the King [Uther] was made known, the bishops of the land came with their clergy and bore his body to the monastery of Ambrius and buried it with royal honours at the side of Aurelius Ambrosius, inside the Giants’ Ring. [VIII.24]

Geoffrey’s Mount Ambrius is a large monastery. Traditionally, Guevenere is said to have fled to a convent at Amesbury, though in Geoffrey she goes instead to the CITY OF THE LEGIONS and enters a convent there. There was a convent at Amesbury in Geoffrey's day, founded in the 10th century. Today, the Abbey Church of St. Mary and Melor still stands: the oldest part is a 12th-century nave, probably built on the foundations of the Saxon church.