The four stirrup towers are two storeys tall, across internally, with walls, flat at the front and curved at the back. They would originally have been topped by firing platforms, with gunloops around the inside of the fortification enabling their occupants to fire into the courtyard if necessary. The bastions built around the outside of the towers in the third phase of work are wide internally and each extend from their respective stirrup tower, with walls. Most of the bastions had a single internal gun room with a robust gun deck on top, but the West Bastion was used as a kitchen and the interior was fitted with two circular ovens and a range for cooking. The bastions would have been connected by a wall-walk and parapets, but these have since been lost. The south stirrup tower and bastion remains partially buried as a result of the construction of the Rampire.