authorship of the work and the period of its writing are open questions for modern historians. There are several extant manuscript versions of the work, varying in details. The most important ones have been dated to between the 9th and the 11th century. Some modern scholars think it unlikely that the work was composed by a single writer or compiler, suggesting that it may have taken centuries to reach its final form, though this theory is not conclusive. In Chapter 31, we are told that Vortigern ruled in fear of Ambrosius. This is the first mention of Ambrosius in the work. According to Frank D. Reno, this would indicate that Ambrosius's influence was formidable, since Vortigern considered him more of a threat than northern invaders and attempts to restore Roman rule in Britain. The chapter relates events following the end of Roman rule in Britain and preceding Vortigern's alliance with the Saxons. The most significant appearance of Ambrosius is the story about Ambrosius, Vortigern, and the two dragons beneath Dinas Emrys, "Fortress of Ambrosius" in Chapters 40–42. In this account, Ambrosius is still an adolescent but has supernatural powers. He intimidates Vortigern and the royal magicians. When it is revealed that Ambrosius is the son of a Roman consul, Vortigern is convinced to cede to the younger man the castle of Dinas Emrys and all the kingdoms in the western part of Britain. Vortigern then retreats to the north, in an area called Gwynessi. This story was later retold with more detail by Geoffrey of Monmouth in his fictionalised Historia Regum Britanniae, conflating the personage of Ambrosius with the Welsh tradition of Myrddin the visionary, known for oracular utterances that foretold the coming victories of the native Celtic inhabitants of Britain over the Saxons and the Normans. Geoffrey also introduces him into the Historia under the name Aurelius Ambrosius as one of three sons of Constantine III, along with Constans and Uther Pendragon. In Chapter 48, Ambrosius Aurelianus is described as "king among all the kings of the British nation". The chapter records that Pascent, the son of Vortigern, was granted rule over the regions of Buellt and Gwrtheyrnion by Ambrosius. Finally, in Chapter 66, various events are dated from a Battle of Guoloph (often identified with Wallop, ESE of Amesbury near Salisbury), which is said to have been between Ambrosius and Vitolinus. The author dates this battle as taking