A planned town (bastide) was laid out at the same time as the castle. The Anglo-Norman borough was an attempt by Edward I to pacify the Welsh.
Denbigh Castle, which was built during two phases, was based on designs attributed to Master James of St George. In the first period, commencing 1282, parts of the outer ward were constructed. These outer defences included the southern and western walls and the eastern towers. Later work on the inner ward began including parts of the curtain wall and the castle's main gatehouse. The borough's new town walls were also began during this period.
But in 1294 Denbigh was attacked and taken during the revolt of Madog ap Llywelyn halting the work on the incomplete town and castle. Following its recapture a year later, Henry de Lacy substantially revised the plans in the second phase of building work. This time the inner ward's curtain wall were refortified with thicker and higher walls.
Historian John Goodall remarked that the entrance is "the most architecturally sophisticated gatehouse of the thirteenth century". The main gatehouse was heavily buttressed with a three octagonal towers and a drawbridge: two towers faced outwards and a third interior tower, (the Badnes Tower), inside the main gateway. This three-towered triangular gatehouse now created a heavily defended passageway that had murder-holes, portcullises in series, two wooden doors, and enfilading arrowslits. One gatehouse tower contained the porter's lodgings while the other served as the prison.