Mars Defense Perimeter platforms were large unmanned defense platforms. The Mars Defense Perimeter in the Sol system included hundreds of these platforms just beyond the orbit of Mars and near the system's asteroid belt. (The Dominion War Sourcebook: The Fires of Armageddon) The platforms were unable to hold off the Borg attacks in 2367 and 2373. Following the second attack they were upgraded, though it was still not enough to stop the massive Breen attack in 2375. However, without the system the casualties on Earth would have likely been significantly higher.