Between the 16th and 17th century, the construction of a system of fortified structures that would be the nucleus of the Fortress of São Filippe/São João Baptista do Monte Brasil. Its main fortification hugs the northern slope of Monte Brasil, but includes of redoubts, emplacements and garrisons around the flanks of the volcano, including the Fort of Zimbreiro, Fort of Santo António, Fort of São Diogo and Fort of Quebrada. Many of the road accesses to Pico do Facho, Pico das Cruzinhas and Pico do Zimbreiro, in addition to the caldera and coastal forts were opened during this period, giving access to most of the peninsula. On Pico do Facho, starting in this period and extending to the 20th century, was a house and semaphore signalling post along with several military structures, including excavations in the ground (channels and rectangular depressions) representing complex installations associated with these activities.