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Aurelius Ambrosius

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Relatively few characters from the Arthurian legends can be definitely confirmed as historical. Aurelius Ambrosius is one of them. He was Arthur’s legendary uncle and he had a large part to play in the founding of Arthur’s dynasty and also in the war against the Saxons.


Aurelius Ambrosius

The earliest account which gives direct details about Ambrosius’s lineage is the Historia Brittonum of the ninth century. Ambrosius is mentioned several times in this work. One of them makes a reference to his father being a consul. This ties in with an even earlier reference by the sixth century Gildas to Amrbrosius’s parents having ‘worn the purple’. Purple was a colour that was worn by those in various different prominent positions in the Roman Empire, including consuls. So the claim found in the HB about Ambrosius’s parentage is plausible.

The next source to give more information about Ambrosius’s family is Geoffrey of Monmouth’s 12th century Historia Regum Britanniae. According to this, his father was Constantine, the king of Britain. This character is traditionally identified as the historical Constantine III, the usurping emperor of Britain and Gaul in the early fifth century (however, there are reasons for doubting this identification). An emperor could also be a consul, and Constantine III did hold that position in 409.

On the other hand, if Ambrosius’s father was actually a different Constantine who ruled as some kind of king in Britain in the early fifth century, then he could well have been a consul within Britain (for there is evidence that the Britons kept the position of consul even after they broke away from the Roman Empire). In any case, Ambrosius’s father was allegedly named Constantine, whether that was the historical Constantine III or a different man of the same name.

According to the HRB, Ambrosius was the middle of three brothers. His older brother was Constans, while his younger brother was Uther. Constans spent his youth as a monk. However, after his father was killed, he became the king of Britain. Sometime later, he was also killed, murdered by Vortigern. At this point, Ambrosius and his brother Uther were taken away to Britanny for protection, and this is where Ambrosius grew up.

There is no direct record in any legend of Ambrosius marrying and having children. However, Gildas mentions his descendants in his time, so we know that he must have had children.

Ambrosius’s younger brother Uther was, of course, the father of King Arthur. This makes Ambrosius the paternal uncle of Arthur.

Early Years

One particularly famous episode in the Historia Brittonum concerns the building of a tower by Vortigern’s men. In this account, a young boy is brought to the tower to be sacrificed so as to stop the tower from constantly collapsing, but he manages to outwit Vortigern’s wise men by progressively revealing what is underneath the tower and actually causing it to collapse. The boy tells his name to Vortigern, revealing that he is Ambrosius.

In this source, the young Ambrosius is found in and taken from Glywysing (roughly modern-day Glamorgan). Thus, it is likely that Ambrosius’s family had some connection with this area.

At the end of the account, Vortigern cedes all of western Britain to Ambrosius. This perhaps indicates that the origin of this fanciful encounter was a real battle between of some kind between a young Ambrosius and Vortigern’s forces.

Interestingly, the Historia Brittonum records a battle between Ambrosius and a man named Vitalinus. This is said to have taken place in 437. This would have had to have been when Ambrosius was young, probably in his late teens (see ‘When He Lived’ below). The identity of Vitalinus is difficult to ascertain, but he appears to be connected to Vortigern in some way (a form of the name appears as the name of Vortigern’s father and grandfather in the HB, indicating that it was a family name).

Therefore, the fanciful story of Vortigern and the young Ambrosius, which ends in Vortigern ceding a large portion of Britain to the youth, might come from this historical encounter between a teenage Ambrosius and the forces of Vortigern in 437, resulting in a victory for Ambrosius.

Nonetheless, the HRB claims that Ambrosius grew up in Brittany and only permanently returned when he began his campaign against the Saxons and slew Vortigern (which, as we will see later, took place well into the second half of the fifth century). So it appears that Ambrosius might have returned to Brittany soon after this victory against Vitalinus, holding only nominal control over western Britain, or a large portion thereof.

This makes more sense of the HB’s statement that Vortigern spent his reign in fear of Ambrosius than the idea that Ambrosius never stepped foot in Britain from the time he left as a child until he finally returned to slay Vortigern.


Aurelius Ambrosius

After the massacre of the British leaders by the Saxons, Ambrosius decided to return to Britain to avenge this massacre. He and his brother Uther returned and fought very effectively against their enemies. Firstly, they attacked Vortigern, pursuing him to his castle in Wales. They burned the castle to the ground, killing Vortigern.

After this, Ambrosius and Uther began a campaign against the foreign invaders. The Saxons were in fear of the British leader, and they fled to the north, past the Humber. Ambrosius won the following battle, though Hengist (the Saxon leader) was still alive and managed to reposition his army elsewhere. At the second battle, Ambrosius was able to win with the help of troops from Brittany. After killing Hengist, he pardoned the two other Saxon leaders, Octa and Eosa, after they submitted to his rule.

From this point on, Ambrosius was the new high king of the Britons. His reign was not a lengthy one, so there are not many events which took place during it. One of the only other notable events is the construction of a stone monument to memorialise the slain British leaders from the peace conference. Merlin and Uther were sent by the king to Ireland to recover an existing stone monument, called the Giants’ Dance. This was then taken to Britain and established by the site of the peace conference (evidently intended to be Stonehenge).


Near the end of his life, for some reason not revealed in the HRB, Ambrosius was confined to a sickbed. During this time, his brother Uther was entrusted with the care of the kingdom. Taking advantage of his vulnerable state, the Saxons craftily poisoned him by the hand of a man named Eopa, ending his life. Uther then officially succeeded him as high king of the Britons.

When He Lived

The earliest account of Ambrosius is Gildas’s mention of him. Although this writer did not give an extensive amount of dating information, he did tell us enough to work out the general period in which Ambrosius must have lived. He tells us that Ambrosius was the military leader who led the Britons against the Saxons before the Battle of Badon was fought (and possibly during that battle too, but see ‘Victor at Badon?’ below).

The Saxons were brought to Britain in 428 according to the Historia Brittonum. This date is seemingly confirmed by the fifth-century Life of Germanus, which records that the Britons were fighting against the Saxons as early as c. 431. The Gallic Chronicle of 452 also testifies to the Saxons having gained a considerable amount of British territory by 441.

According to later legend, Ambrosius was just a child when Vortigern came to power, which was shortly before the Saxon conquest began. This would indicate that his birth took place in about the first quarter of the fifth century. More specifically, the Historia Brittonum claims that Vortigern rose to power in 425. If Ambrosius was a child at that time (just ‘a child in his cradle’ according to the HRB), then we can estimate that he was born in about the year 420.

This estimate accords with the other information about when this commander lived. Bede speaks of him as beginning his campaign against the Saxons in the reign of Zeno, which could mean anywhere from 474 until 491. Since Ambrosius was (according to the HRB) raised in Brittany and only returned to Britain when he was motivated to stop the Saxons after the massacre of the British leaders, this large gap between 420 and 474 is quite feasible.


As mentioned before, Gildas wrote about Ambrosius. After referring to the fact that the Saxons savagely wrought destruction to the Britons and sent them fleeing to the mountains and the forests, Gildas tells us this:

“The poor remnants of our nation… took arms under the conduct of Ambrosius Aurelianus, a modest man, who of all the Roman nation was then alone in the confusion of this troubled period by chance left alive.”

As we can see, it appears that the historical name of this leader was actually ‘Ambrosius Aurelianus’ as opposed to ‘Aurelius Ambrosius’. The form ‘Aurelius Ambrosius’ was used at least as early as Bede, and that is the form that most subsequent sources use.

But the primary point to be taken from this quote is the fact that Ambrosius was almost certainly a historical figure. Gildas lived less than a century after the events he describes, and he refers to the living descendants of Ambrosius and comments on their moral character. So we can be very confident in the historicity of Ambrosius.

As to his alleged descent from Constantine the king of Britain, this is difficult to determine without being absolutely certain which Constantine is meant. If it was Constantine III, the emperor of Britain and Gaul, then Ambrosius could not have been born any later than the year 411, when this Constantine is historically known to have died. This would mean that Ambrosius would have been about 27 years old at the time of his battle against Vitalinus in 437. That is a reasonable age.

However, this would mean that when he first took charge of the Britons and started leading them against the Saxons (which was in the mid-470s at the earliest), Ambrosius would have been in his sixties. This is possible, though an earlier age is more likely. In addition, it would not make him an infant at the time Vortigern took power, in 425.

If we conclude that Ambrosius was actually the son of a different Constantine (remembering that the Constantine of the HRB bears almost no similarity to the usurper of Roman history), then we could plausibly extend his birth year to just a few years before the start of Vortigern’s reign. This would match the information about him being an infant when the wicked ruler took power. So, an estimate of about 420 seems most likely in view of that information.

This would make Ambrosius 17 years old when he fought against Vitalinus. Admittedly, this is young, but not implausibly so. More importantly, it is a better fit with the earlier information provided by Bede regarding Ambrosius leading the Britons against the Saxons from the mid-470s at the earliest. A birth year of 420 would place Ambrosius in his fifties at this time, which is more plausible than the previous suggestion.

All in all, it appears that Ambrosius may well have been the son of a Constantine, but it was most likely not Constantine III.

What about the claim that he was the older brother of Uther Pendragon and thus the uncle of King Arthur? These claims are not necessarily dependent on each other, so let us consider them individually.

Firstly, is it plausible that Ambrosius really was the older brother of Uther? Significantly, Gildas claims that Ambrosius was ‘of all the Roman nation then alone in this troubled period’. This would seem to exclude the possibility that he had a brother who was fighting alongside him during that period.

However, as mentioned before, Gildas does reveal that Ambrosius had descendants. Since the legends speak of Uther succeeding Ambrosius, could it be that they were actually father and son, rather than brothers? It is a possibility. Alternatively, it may be that they were not actually related by blood, and that Uther was merely the brother-in-law of Ambrosius. In any case, the information Gildas tells us does make it very unlikely that Uther was related to Ambrosius in the way the legends claim.

What about the second matter, that of Ambrosius’s connection to Arthur? Is it reasonable to believe that they really were relatives, as the legends claim? While it does not seem possible that the former really was the latter’s paternal uncle (for the reasons related to Uther discussed above), there is nothing inherently unlikely about a familial connection of some kind between the two men.

We know that Ambrosius had descendants who were still active in Gildas’s time, so the idea that Arthur was actually the son or the grandson of Ambrosius (forming the linking generation between Ambrosius and his descendants in Gildas’s time) is quite an appealing one. It harmonises the legend of them being related with the historical information mentioned by Gildas.

Given that Ambrosius must have had children, it would be wholly logical for one of them to have succeeded to the throne, assuming that Ambrosius really was a king and not just a military commander (he is called ‘the great king among the kings of the Britons’ as early as the Historia Brittonum). Thus, we would very logically expect a son or grandson of Ambrosius to have been reigning among the Britons in the sixth century, exactly the time in which Arthur was supposed to have been commanding them.

This line of reasoning indicates that the idea that Uther was Ambrosius’s son is more plausible than them being brothers-in-law. It would be perfectly logical for Uther to succeed his father, but not so logical for him to succeed his brother-in-law. Since we know for sure that Ambrosius did have descendants, it thus seems that the most likely scenario is that Uther was his son, and therefore Arthur was actually his grandson rather than nephew.

So, while the legends do not appear to be perfectly accurate on this point, there is good reason for concluding that there genuinely was a familial relationship between Ambrosius and Arthur.

Victor at Badon?

One major question for researchers of this period is: Who really led the Britons to victory at the Battle of Badon? While this has traditionally been attributed to Arthur, there are a number of scholars who believe that the real victor was Ambrosius. The reason for this is Gildas’s description of the Battle of Badon. It follows on directly from his description of Ambrosius, as can be seen here:

“[The Britons] took arms under the conduct of Ambrosius Aurelianus, a modest man, who of all the Roman nation was then alone in the confusion of this troubled period by chance left alive. His parents, who for their merit were adorned with the purple, had been slain in these same broils, and now his progeny in these our days, although shamefully degenerated from the worthiness of their ancestors, provoke to battle their cruel conquerors, and by the goodness of our Lord obtain the victory. After this, sometimes our countrymen, sometimes the enemy, won the field, to the end that our Lord might in this land try after his accustomed manner these his Israelites, whether they loved him or not, until the year of the siege of Bath-hill [Mount Badon], when took place also the last almost, though not the least slaughter of our cruel foes.”

It is understandable why some researchers conclude that Gildas was attributing the battle to Ambrosius. It certainly could mean that. Under this interpretation, the battle was falsely attributed to Arthur at a later date.

However, is it necessarily the case that Arthur’s greatest victory was not his, but actually Ambrosius’s? While the words of Gildas allow for that interpretation, it must be emphasised that his words definitely do not make the matter clear. When he mentions the fact that ‘sometimes the Britons, and sometimes the Saxons’ were victorious until the Battle of Badon, this easily allows for a long period of time in which the Britons (and the Saxons, for that matter) followed various different commanders.

There is actually reason to believe that Ambrosius could not have been the victor at Badon. Recall that he was likely born in c. 420. The Battle of Badon, meanwhile, is generally thought to have occurred in c. 500 or a decade or two later (the Annales Cambriae places it in 516).

If we use the earlier date, this would make Ambrosius 80 years old at the time of the battle. Using the later date of 516 would make Ambrosius nearly 100! Obviously, if the date of c. 420 for Ambrosius’s birth is correct (and the fact that he fought a battle in 437 strongly suggests that it could not have been any later), then Ambrosius simply cannot have been the victor at Badon.


A more realistic theory about Ambrosius is that he was identical to Riothamus. This fifth-century historical figure is known to have fought a battle against the Visigoths in Gaul in 470. He lost the battle, although he himself did not perish. The historian Jordanes described Riothamus as ‘king of the Britons’, though it is debated whether he meant the Britons of Britain or the Britons of Brittany.

Many people have attempted to identify this historical king with Arthur himself, but the reasons for doing so are very weak and do not stand up to scrutiny (see the article ‘King Arthur’). One of the problems is that Riothamus lived too early to have been identical to Arthur. However, he is a perfect chronological match for Ambrosius.

Consider: Ambrosius was supposedly away in Brittany from 425 (when Vortigern took power) until the mid-470s (when he returned to fight against the Saxons). He was allegedly the heir to the throne of Britain, the son of the former high king. And over in Gaul we have a figure who was potentially the king of Brittany with a name that may actually have been a title meaning ‘Kingliest’ (although some researchers believe that ‘Riothamus’ was a proper name). The year of 470 for his battle against the Visigoths places him in Gaul in the period in which Ambrosius was there.

So, could Riothamus have actually been Ambrosius? It is certainly a possibility. It is a much more appealing theory than identifying Riothamus with Arthur. However, one of the same issues with the Arthur identification also applies here. There is some reason to believe that Riothamus was not a title, but was actually the man’s name. It is used in personal correspondence between him and Sidonius Apollinarius.

If this is so, then this would appear to disprove the theory that Riothamus was Ambrosius; unless, ofcourse, he was known by more than one name, which is possible.

In truth, the theory has a fairly weak foundation to start with. There are not a whole host of similarities between Riothamus and Ambrosius, but only a few. Nonetheless, this theory remains a distinct possibility, albeit not necessarily a very likely one.

Final Thoughts

In conclusion, we can see that Ambrosius was a very powerful figure of the fifth century. It appears that he was born in about 420 and had to be taken away to Brittany for protection from Vortigern, due to being the true heir to the throne. It is possible that he returned in his youth to battle against Vortigern and gained some territory in Britain, causing Vortigern to dread him for the extent of his reign. However, it appears that Ambrosius spent most of his life in Brittany.

Eventually, after the situation with the Saxons in Britain got too out of hand for Ambrosius to allow, he returned to Britain and fought alongside a man who may have been his brother-in-law or son. They killed Vortigern and then crushed the Saxons, crippling the Saxon advance for a time.

It appears that Ambrosius’s father should not be identified with Constantine III, but should be identified with a different man of the same (or a similar) name who lived slightly later. Although Ambrosius was most probably not the brother of Uther, it is reasonable to believe that he really was related to Arthur in some way, perhaps being his grandfather.

We have also seen that there are a number of different theories about Ambrosius, such as the theory that he was actually Riothamus or the theory that he was the true victor at Badon. Neither of these theories are amazingly likely, though the former is more likely than the latter. But clearly, Ambrosius is a figure around which many theories could be created, and undoubtedly more theories about him will arise in the future.