Mountain castle with two defence enceintes

This relief model illustrates a mountain castle that was probably already in existence in Leonardo's day. Leonardo made improvements in it, with a view to increasing its resistance to the new, powerful firearms that were introduced in the second half of the 1400s. The ravelin was probably located in defence of an entrance at the base of the castle - the entrance being indicated by the caption, sotterranea "underground passage". The ravelin consists of three towers with very steep scarps that give way to a masonry curtain with a raised way, and a buttress at the centre - the angle being of 125°. The two concentric walls stand in defence of the sturdy tower at the centre, which was probably where the lord of the manor lived.