The Oxford Castle was originally constructed by baron Robert O'Dyly in the aftermath of the 1066 Norman conquest. O'Dyly chose the western edge of the town in order to make use of its stream as a natural defence. St George's tower – the castle's tallest and oldest, was constructed to protect any western invasion to the town.

The castle has a history of warfare having been besieged in the War of Anarchy, Barons War and English Civil War to name but a few. Each battle brought with it destruction and damage to the castle resulting in extensive repairs and significant improvements. Over time, as civil strife dissipated, the castle was no longer needed to protect the city. In the 1750s the castle was converted to a prison. Walls – which for centuries had kept aggressors out, were now used for keeping aggressors in.

The prison was closed in 1996. Since then, the 'Malmaison' chain has opened a hotel in part of the former prison blocks. Visitors can access a guided tour of the old castle crypts and grounds at 'Oxford Castle Unlocked.'