To understand why there is a problem with the birthdate of Arthur ap Pedr given by Bartrum, i.e. 560, we need to look at a manuscript that mentions this individual. My allocation of the generation numbers are in the first column and they are based on the principle that the generation number of an offspring should be one greater than that of the parent. The generation number in the fourth column are those given by Bartrum. The first table shows the first part of the Demetian pedigree. The obits shown in the third column are those stated by Bartrum and originate from the Annales Cambriae.
|Gen.||HG 2a||Obit acc. Bartrum||Gen. acc. Bartrum||Birthdate acc. Bartrum|
Using my generation numbers, regression analysis of the five obits in the above table give a generation step-size of 28 years. On the basis of this statistical technique and on the assumption that the average life expectancy was 65 years, it follows that an estimate of Arthur’s birthdate is 531, not 560 as stated by Bartrum.
Using a much larger database of obits the step-size is 32 years. This is consistent with Bartrum who wrote:
“This is based on the well known fact that, on the average, three male generations span almost exactly a century.”
After which he added the note:
“A male generation is the period of time between the birth of father and the birth of son, or daughter. Female generations, birth of mother to birth of son or daughter, are on the average much shorter, and in the period covered are nearer to 20 years, i.e. five to a century.”
The vast majority of generations in my database are male ones.
The larger database gives Arthur’s birth as occuring c. 487, this being the mid-value in the range for gen. 0. The Demetian Arthur’s birthdate is in the period that one would expect for the individual around whom the Arthurian cycle was built. A birthdate of rounded figure 490 would be reasonable on the basis of the dates for Badon and Camlan given in the Annales Cambriae.
Using my generation numbering, Bartum’s estimates for the birthdates from Cyngar to Owain in the above table has an average step-size of 26 years, which is far too small. To achieve a more realistic step-size, he has given a number of parents and offsprings the same generation number, viz. Elen/Owain, Cadwgon/Rhain and Nowy/Gwlyddien. This results in a more satisfactory step-size of 33 years, but at the cost of artificially giving parents and offsprings the same generation number.
The reason why Bartrum’s analysis went astray may have been because he believed that HG 2 was a single pedigree list, whereas in reality it consists of three seperate segments. That the manuscript compilers did not always know when one list ended and the next one began can be seen in, for example, JC 10 to 11 where the ending of the first list is repeated in the start of the following one. In the second segment of HG 2, shown below, he made use of two dateable events, namely the birth of Gwerthefyr and that of Macsen Wledig. In the Harleian document itself there names take the form Guortepir and Maxim gulecic respectively.
|Gen.||HG 2b||Obit acc. Bartrum||Gen. acc. Bartrum||Birthdate acc. Bartrum|
Gildas writing in the 540s in the De Excidio describes Gwerthefyr, whose name takes the form Vortipor, with the words
“… though thy head is now becoming grey … though the end of life is gradually drawing near …”.
So, Bartrum’s birthdate for him of 480 cannot be too wrong. He errs when he identifies the Maxim Wledig with the Roman emperor Magnus Maximus who died in 388. That individual, who the Welsh called Macsen Wledig, belonged to gen. -4, see the table below. This forces him to use an average generational step-size for the second segment of 21 years, which is not credible. Again, he circumvents this problem by giving Clodri/Tryffin and Annun/Ednyfed the same generation number, resulting in a step-size of 30 years.
Maxim Wledig was a reference to the emperor Constantius Chlorus who died in 306, which is in line with him being in gen -7. His wife was Helena. This tallies with the first part of the Mabinogion tale entitled the Dream of Macsen Wledig in which Macsen came to Britain and married Elen Luyddog, the daughter of Eudaf.
It will be noted that there is an anomaly in that Bartrum’s tentative birthdate given to Clodri is 10 years after that of Tryffin who Bartrum believed was his nephew.
The third and last segment, HG 2c, is shown below. Note, the missing names that have been inserted, i.e. Custennin and Macsen Wledig, can be seen in JC 13b.
|Gen.||HG 2c||JC 13b|
|-6||Constantini magni||Constantinus mawr|
|-4||[Macsen Wledig]||Maxen wledic|
This segment supports the identification of the Maxim with Constantius Chlorus as both appear in gen. -7. The latter individual’s wife, St. Helena, has been conflated with Eudaf’s daughter, Elen Luyddog who was probably St. Helena of Cornwall.
It may be that Barturm, too, noticed HG 2 need to be divided into three segments as he wrote:
“There seems to be three independent strands of pedigree here, see note to ABT 18a.”
 Bartrum, P.C., 1974, vol. 1, 6.
 Bartrum, P.C., 1966, 126.