The Alps are one of the great mountain range systems of Europe stretching approximately 1,200 kilometres (750 mi) across eight Alpine countries from Austria and Slovenia in the east, Switzerland, Liechtenstein, Germany, France to the west and Italy and Monaco to the south. The mountains were formed over hundreds of millions of years as the African and Eurasian tectonic plates collided. Extreme shortening caused by the event resulted in marine sedimentary rocks rising by thrusting and folding into high mountain peaks such as Mont Blanc and the Matterhorn. Mont Blanc spans the French–Italian border, and at 4,810.45 m (15,782 ft) is the highest mountain in the Alps. The Alpine region area contains many peaks higher than 4,000 m (13,123 ft), known as the "four-thousanders".[source]