Central System

The eastern Central System stretches through the mountains of Somosierra and Ayllón, separating the Castilian plains from the valleys to the south. Roads must find their way through high passes between the ridges. At Somosierra, Spanish forces attempted to block Napoleon's advance on Madrid in 1808. French troops, supported by Polish light cavalry, forced the pass in a fierce battle, opening the way toward the capital during the Peninsular War.