Chepstow Castle - Norman Stone Wall

The stone wall of the 11th-century Norman hall has courses of red Roman brick within it. These had been used as levelling courses in the stone wall. Where had this Roman brick come from? The intriguing thing is that either there might have been an important and large Roman building nearby or perhaps it was brought from the Roman town of Caerwent or Roman fortress of Isca at Caerleon.