Feature 'f' is a hornwork[1]HornworkThe Weber Church of Zittau inside a hornwork[2]Drawing, showing a hornwork, of the fortress Nya Älvsborg in Gothenburg, Sweden from 1811.
A hornwork is an element of the Italian bastion system of fortification. Its face is flanked with a pair of demi-bastions.
It is distinguished from a crownwork, because crownworks contain full bastions at their centers. They are both outworks.
