Abundant natural resources in and around the Menai Straits enabled human habitation in the area during prehistory.
The Ordovices, a Celtic tribe, lived in the region during classical antiquity.
The Romans and occupied the region until their departure in the 5th century, after which Caernarfon became part of the Kingdom of Gwynedd.
In the late 11th century, William the Conqueror ordered the construction of a motte at Caernarfon, as part of an attempt at conquering the region.
He was unsuccessful and most of Wales remained independent until around 1283.
In the 13th century, Llywelyn ap Gruffudd, ruler of Gwynedd, refused to pay homage to Edward I prompting the English conquest of Gwynedd.
It was in the same year, Caernarfon was made a borough, a county and market town, and the seat of English government in North Wales.