As the dust started to settle among the hills and mountains, tribal groups clustered among them. As in any culture, when you first meet, you ask "What is your name?", and "Where are you from"? In the earliest days, it was common to give your name and some sort of physical description. This might be like...Peter, the Tall, or Peter, The Short, or David The Red Headed, or David with the Dark Skin. As the families became more organized and settled, and their history more prolonged, the founding fathers (tribal leaders) would become more important. "Who was your father?" came to be extremely important, especially if you had a score to settle or reprisal to take.
On the island, the Picts appear to be the first group to adapt the system of linking their name to that of their father. Drust Mac Erp is the earliest to recorded such a name, living around 449 A.D. Here, Mac means "son of", thus Drust is the son of Erp.(p.169)[These names are taken from a reference called "British Kings & Queens, by Mike Ashley, Barnes & Noble, 1998. The page numbers from this reference are given.] It was some 80 years later that around 530 A.D. Cynlas ap Owain appears in the Welsh Kingdom of Powys.(p.150) This is closely followed by:
Erbin map Custennyn, 540 A.D., from the south-east and south-west (p.116)
Bodgu ap Serguil, 560 A.D., from Ceredigion and Seisyllwg, (p.130)
Meurig ap Tewdrig, 580 A.D., from Gwent and Glywysing, (p.125)
Beli ap Rhun, 580 A.D., from Venedotia and Gwynedd, (p.144)
Owain map Urien, 590 A.D., from northern Britain, (p.106)
From this listing, it can be seen that this system of naming had taken root before 600 A.D. The Welsh system became "ap" (before a constant), and "ab" (before a vowel) to mean "the son of".