The Matterhorn acquired its characteristic pyramidal shape in much more recent times as it was caused by natural erosion over the past million years. At the beginning of alpine orogeny, the Matterhorn was only a rounded mountain like a hill. Because its height is above the snowline, its flanks are covered by ice, resulting from the accumulation and compaction of snow. During the warmer period of summer, part of the ice melts and seeps into the bedrock. When it freezes again, it fractures pieces of rock because of its dilatation (freeze-thaw), forming a cirque. Four cirques led to the shape of the mountain. Because of its recognizable shape, many other similar mountains around the world were named or nicknamed the 'Matterhorn' of their respective countries or mountain ranges.