King Ambrosius Aurelianus
(Born c.AD 403)
(Welsh: Emrys; Latin: Ambrosius; English: Ambrose)

Ambrosius Aurelianus (or Ambrosius Aurelius) was a British military leader known to the Welsh as Emrys Wledig (the Imperator) or occasionally Emrys Benaur (the Golden-Headed). He is referenced by Gildas as as early as the 6th century when the Britons "challenge[d] their [the Anglo-Saxons'] victors to battle under Ambrosius Aurelianus. He was a man of unassuming character, who, alone of the Roman race, chanced to survive the storm in which his parents, people undoubtedly clad in the purple, had been killed". He is thus already depicted as a challenger to the British authorities. Nothing is known of his parentage except for the unlikely details provided by Geoffrey of Monmouth, who tells us that Ambrosius was the second son of the Emperor Constantine. Within thirty years, however, Welsh Arthurian legends had identified Geoffrey's Constantine with Constantine Corneu, the King of Dumnonia, despite the clash in their ancestry.

Geoffrey further tells us how Ambrosius was still a young child when his teenage brother, Constans' short-lived reign came to an abrupt end. With his father executed and his brother murdered, little Ambrosius, along with his brother, Uther, was said to have been bundled up and taken across the Channel to the safety of the court of his cousin, King Budic I of Cornouaille in Brittany. There he grew up, while the 'evil' King Vortigern reigned in Britain; but, traditionally, Ambrosius always planned to return and claim his rightful inheritance.

His chance is said to have arrived some years later, when Geoffrey says Ambrosius returned to Britain, landing at Totnes in Devon. It may be at this point in his story that the 9th century historian, Nennius, tells us in his Historia Brittonum that Ambrosius (who he describes as the son of a Roman consul) clashed with a certain Vitalinus (probably Vortigern himself or a close relative) at the Battle of Guoloph (probably at Nether Wallop in Hampshire). This may have resulted in victory for Ambrosius who Nennius also recorded as one of the chief 'dreads' of King Vortigern. The two seem to have later come to some sort of agreement with one another whereby Ambrosius received control of "all the kingdoms of the western side of Britain" in a division reminiscent of the Roman Empire. His capital was apparently the fortress at Dinas Emrys, just west of Beddgelert in North Wales. Nennius tells the usual tale of the hillfort's origins but confuses the fatherless boy, who is usually given as Myrddin/Merlin, with Ambrosius himself.

Ambrosius may well have been unsatisfied with such a compromise, however, and Vortigern's pro-Anglo-Saxon policies eventually led to his downfall. The British people finally rallied behind Ambrosius and Vortigern was, traditionally, hounded into fleeing to the refuge in his mountain strongholds. While under siege in Caer-Guorthigirn at Little Doward (at Ganarew in Herefordshire, north-east of Monmouth) or Tre'r Ceiri, above Llanaelhaearn in Lleyn, the fortress was miraculously struck by lightning. Vortigern and his entire garrison were burnt to death.

After Vortigern's demise, Nennius says that Ambrosius was conciliatory towards the former's sons. Pasgen was allowed to keep his lands in Buellt and Gwerthrynion, and this may also have been true of his brothers in Gwent and Powys. However, Geoffrey seems to have misunderstood this information and says, instead, that Pasgen rebelled against Ambrosius and twice attempted to overrun Britain with help from the Anglo-Saxons and the Irish. Gildas tells us that, "From that time the citizens were sometimes victorious, sometimes the enemy". Geoffrey gives further details with no justification. He tells how the main Anglo-Saxon forces had retired north of the Humber, where Ambrosius later met Hengist in Battle at Maesbeli and then Caer-Conan (Conisburgh). Then he is said to have besieged Octa and Osla at Caer-Ebrauc (York). All were defeated, but Ambroius let them settle their people in Bryneich (Bernicia).

Geoffrey then moves into a flight of fancy about the origins of Stonehenge, which he calls the Giant's Ring. Presumably this was because it stands near Amesbury which is generally thought to have been named after an Ambrosius/Emrys if not the famous one. Geoffrey calls Salisbury Plain, Mount Ambrius (which is a little odd) and claims that Stonehenge was built as a memorial to those massacred by the Anglo-Saxons at the 'Night of the Long Knifes' during King Vortigern's reign. He was also supposed to have been buried there himself after being poisoned by an Anglo-Saxon at Caer-Guinntguic (Winchester).