Return and take the path to your left going up the slope. Turn right at the top and go to the large Information board around the circle of trees.
The chronicler, William of Malmesbury, tells us Queen Matilda came to Calne in 1139. In 2010 an archaeological dig uncovered the foundations of a large stone building. It showed that the castle or fortified house stood on the site of former Romano-British buildings. The information board here has more detail.