A crucially important figure in sieges and on battlefields was the cartographer, who drew up maps of fortresses and territories. Starting from the early 16th century, one of the fundamental topographic instruments was the magnetic compass, consisting of a magnetized needle pivoting at the centre of a graduated disk divided into eight sectors and carrying a diopter. Each sector corresponded to the directions of a wind. This instrument had numerous variants: the theodolite, planimeter, holometer and graphometer.