Type of ancient megalithic stone monument (seemegalith). Menhirs were simple upright stones, sometimes of great size, erected chiefly in Western Europe. Arrangements of menhirs often form vast circles, semicircles, or ellipses. Many were built in Britain, the best-known sites being Stonehenge and Avebury in Wiltshire. Menhirs were also placed in parallel rows, called alignments, the most famous being the Carnac alignments in northwestern France, with 2,935 menhirs. These were probably used for ritual processions.