As discussed in the previous post, it is a very common belief that Geoffrey of Monmouth derived most of his information about the Roman period of Britain from Nennius's Historia Brittonum, a British work from the ninth century. In that post, I argued that all the evidence indicates that Geoffrey absolutely did not use the information found in Historia Brittonum regarding Julius Caesar's invasions of Britain to create his own account in Historia Regum Britanniae. There is evidence of some slight textual relationship, but the two accounts are clearly very far removed from each other in whatever 'textual family tree' that might exist. Also notable is the fact that, when stripped down to the same level of detail as Nennius's account, Geoffrey's is by far the more accurate. This is illogical if Geoffrey took the information from HB and expanded on it, as is commonly argued. This evidence actually supports the idea that Geoffrey did have a genuine, otherwise-unknown, source that either predated or was simply more accurate than HB.
Now, we will look at the rest of the Roman period from Historia Brittonum, to see whether it is likely that it formed the origin of Geoffrey's account.
After describing Julius Caesar's invasion, here is what Nennius says about the Emperor:
"in honor of him [Julius] the Romans decreed the fifth month to be called after his name. He was assassinated in the Curia, in the ides of March."
This is nowhere to be found in Geoffrey's account. There is extra detail given after the end of the British invasion of 54 B.C.E., but this is not it. Instead, Geoffrey makes reference to Caesar's war against Pompey the Great.
After this, Nennius describes the successful Claudian invasion of 43 C.E., saying:
"He carried with him war and devastation; and, though not without loss of men, he at length conquered Britain. He next sailed to the Orkneys, which he likewise conquered, and afterwards rendered tributary."
Almost all of this is very general, and there is nothing here which is unique to Nennius and Geoffrey, so nothing notable to speak of. Nennius's next line is much more interesting:
"No tribute was in his time received from the Britons; but it was paid to British emperors."
This is not in Geoffrey's account. There are no 'British emperors' at all. If Geoffrey was taking information from Historia Brittonum and expanding it, one would absolutely expect there to be something about British emperors at this point. But there is nothing to that effect in HRB.
The next line in Nennius's account is as follows:
"He [Claudius] reigned thirteen years and eight months. His monument is to be seen at Moguntia (among the Lombards), where he died in his way to Rome."
None of this is present in Geoffrey's account.
Next we find a reference to an event which is not known from contemporary sources, but which is nevertheless not unique to Nennius and Geoffrey - it was known from at least as early as the sixth century. In Nennius's account, it begins as follows:
"After the birth of Christ, one hundred and sixty-seven years, king Lucius..."
Let's take a look at the year first. In HRB, the date of Lucius' death is given as 156 years 'after the Lord's incarnation', whereas Nennius has his baptism as being in 167. For what reason would Geoffrey have intentionally changed this information? Clearly he did not derive his information about dates from Nennius.
"...with all the chiefs of the British people, received baptism, in consequence of a legation sent by the Roman emperors..."
The Roman emperors have nothing to do with it in Geoffrey's version.
"...and pope Evaristus."
In Geoffrey's account, the pope is Eleutherius, not Evaristus.
How can it possibly be believed that Geoffrey created his account of this event as found in HRB from the information about it in HB? Such a conclusion is absurd.
After this comes a description of Septimius Severus's campaign in the north of Britain:
"Severus was the third emperor who passed the sea to Britain..."
Geoffrey calls Severus a senator, not an emperor.
"...where, to protect the provinces recovered from barbaric incursions, he ordered a wall and a rampart to be made..."
There is no rampart in Geoffrey's account, only a wall.
"...between the Britons, the Scots, and the Picts, extending across the island from sea to sea..."
The Scots are not mentioned in Geoffrey's version of this account.
"...in length one hundred and thirty-three miles: and it is called in the British language, Gwal."
None of this information is included in Geoffrey's HRB.
"More over, he ordered it to be made between the Britons, and the Picts and Scots; for the Scots from the west, and the Picts form the north, unanimously made war against the Britons; but were at peace among themselves. Not long after Severus dies in Britain."
The Scots are mentioned not just once but three times in Nennius's version of this event. Yet, once again, Geoffrey makes no mention of them at all.
After this, Nennius describes the usurpation of Carausius:
"The fourth was the emperor and tyrant, Carausius, who, incensed at the murder of Severus, passed into Britain, and attended by the leaders of the Roman people, severely avenged upon the chiefs and rulers of the Britons, the cause of Severus."
This implies that Carausius was already an emperor before he 'passed into Britain'. In reality (and this is accurately conveyed by Geoffrey of Monmouth), he was a Roman soldier who, after being summoned to the capital due to alleged misconduct, retreated into Britain and declared himself emperor there. Additionally, his rulership had nothing whatsoever to do with avenging Severus, and this inaccuracy is not present in Geoffrey's account. So really, Nennius's Carausius is about as different from Geoffrey's as can be (and let it be noted that Geoffrey's version is much more accurate).
After this description of Carausius, HB has this to say about Constantius:
"The fifth was Constantius the father of Constantine the Great. He died in Britain; his sepulchre, as it appears by the inscription on his tomb, is still seen near the city named Cair segont (near Carnarvon). Upon the pavement of the above-mentioned city he sowed three seeds of gold, silver, and brass, that no poor person might ever be found in it. It is also called Minmanton."
After the line 'he died in Britain', none of the information presented here features in Geoffrey's account.
Nennius's account continues:
"Maximianus was the sixth emperor that ruled in Britain. It was in his time that consuls began, and that the appellation of Caesar was discontinued: at this period also, St. Martin became celebrated for his virtues and miracles, and held a conversation with him."
Absolutely none of this is in Geoffrey's HRB. This entire episode in the Roman era of Britain is excluded from Geoffrey's account. It is also significant that Maximianus was not real, once again showing how Geoffrey's account is more accurate than Nennius's, despite, so we are supposed to believe, being little more than an expansion of it.
After this, Nennius includes an abundance of accurate information about the usurper, Magnus Maximus. This is interesting, because it is generally held that Nennius's 'Maximianus' is a duplicate of 'Maximus'. But Geoffrey of Monmouth's 'Magnus Maximus' is actually called 'Maximianus'. So, did Geoffrey pick the name from one emperor in Nennius's account but apply to it the information about the following emperor? No, the far more logical conclusion is that Magnus Maximus was, in some records, mistakenly called 'Maximianus'. Thus, Nennius must have found information about a Maximianus who came after Constantius, but also information about Magnus Maximus. So he wrote about both, not realising they were the same person. In contrast, Geoffrey's source simply used one of those sources that referred to Maximus by the inaccurate 'Maximianus'. He clearly did not get his information from HB.
And then, in HB, we get the inexplicable Severus Aequantius, who doesn't feature at all in Geoffrey's account (nor in any other account, for that matter). Then we have Constantius, who reigned for 16 years, while Geoffrey writes about a Constantine (why would he have changed the name?) who ruled for 10 years.
As with the account of Julius Caesar's invasion of Britain, the only reason Geoffrey's account is generally similar to Nennius's is because they are both talking about real history. But significantly, HB includes a huge amount of material which is not present in HRB - much of which is actually inaccurate - or material which HRB contradicts. The conclusion that Geoffrey used Historia Brittonum as a basis for his account of the Roman era of Britain completely flies in the face of all the facts.
