Just east of the Ruins of St Paul from which it is separated by a pebbled path and picturesque foliage, Monte Fort was built by the Jesuits between 1617 and 1626 to defend the College of the Mother of God against pirates. It was later handed over to the colonial government. Barracks and storehouses were designed to allow the fort to survive a two-year siege, but the cannons were fired only once, during the aborted attempt by the Dutch to invade Macau in 1622.
On the outside of the southeastern wall, about 6m from the ground, under a cannon, is a sealed rectangular opening. This was a door used by soldiers patrolling the old city wall, which used to be connected to the fort at a right angle.