There is a great deal of evidence of prehistoric life in the vicinity of Caernarfon.There are burial chambers such as Bryn Gelli Ddu on Ynys Môn (Anglesey); a tool and implement factory on the slopes of Penmaenmawr and hill forts such as Tre'r Ceiri on Yr Eifl (a three peaked mountain on the Llyn Peninsula which can be seen from the higher parts of Caernarfon). Twthill in Caernarfon is a possible location of a hill fort, but the evidence found for this is scant. 

The Roman Era

It wasn't until 60 A.D. (over a century after Julius Ceaser's first invasion of Britain) that the Romans arrived in North Wales. Their main objective was Ynys Môn (the island of Anglesey), then home of the Druids, teachers and spiritual leaders of the Celtic tribes of Britain and beyond. In about 77 A.D. North West Wales was finally conquered by Suetonius Paulinus, and a fort was established in what is now Caernarfon. This was the western frontier of the Roman Empire which stretched, at the peak of it's power, from the Persian Gulf to Caernarfon.

The Roman fort at Caernarfon was built by about 80 A.D. and was named Segontium. The fort housed a detachment of some 800 men, and from here the Romans were able to keep a watch over both Ynys Môn and the Llyn peninsula. Segontium was occupied by the Romans almost continually untill the end of the 4th century A.D., a period of over 300 years. During this time the original wood and mud fort had been replaced by a complex of stone buildings. Segontium had become the administrative centre for the greater part of North Wales.

The Age Of Princes

Little is know of Caernarfon during this era. The Welsh Princes certainly had a court here, and the ruins of Segontium had a lasting impression on the ledgend of the area.

After the Norman invasion of England in 1066 William the Conqueror was eager to conquer Wales. Hugh Lupus conquered much of North Wales, establishing a motte and baily castle in Caernarfon in 1088 - 1098. This timber and earth castle would have been a far cry from the elaborate stone defences of the Roman fort of Segontium. This Norman occupation of North Wales was short lived, ceasing towards the end of the eleventh century. From that time, Hugh's castle became one of the courts of the Princes of Gwynedd. It was during this era that the name 'Caernarfon' came into being. Giraldus Cambrenis (Gerald the Welshman) states in his "Itinary" that he passes through "Caer-yn-arfon" on his tour through Wales (1188) preaching the crusades.

 Edwardian

This is the period that marks the beginning of Caernarfon as a town. After the death of Llywelyn ein Llyw Olaf (the last) in 1282 Edward I of England was eager to consolidate his conquest by establishing an 'iron ring' of castles along the North Wales coast. Thus the Royal Boroughs of North Wales came into being; they were the centers of English influence, military and commercial. Caernarfon was granted it's foundation charter in 1284. The castle itself was not completed until about 1322, and there is evidence that further work was contemplated, yet never started.

Generally speaking the castle design may be said to have some eastern influence in it, attributed to the fact that Edward I served in the Crusades - where he probably saw castles built upon the direct Roman tradition. That tradition had survived in the eastern half of the Roman empire, but had vanished in the west. It is said that Edward I's son, later to become Edward II, was born in Caernarfon. This Edward was the first English Prince of Wales. It is said that Edward I promised the Welsh nobility that he would apoint a Prince to govern them who was Welsh born, of unblemished character and who spoke not a word of English; he the presented the new Prince of Wales - his own infant son born, only a few days old.