Task: Question Generation
Input (English): Archaeological finds suggest that the area has been inhabited since the stone age. Following the Roman invasion of Britain in AD 43 and the conquering of the local Britons in 70 AD the fortress settlement of Clausentum was established. It was an important trading port and defensive outpost of Winchester, at the site of modern Bitterne Manor. Clausentum was defended by a wall and two ditches and is thought to have contained a bath house. Clausentum was not abandoned until around 410.
Output (English): In addition to two ditches, what was Clausentum's defense from invaders?