A menhir is a large upright standing stone. Menhirs may be found singly as monoliths, or as part of a group of similar stones. Their size can vary considerably; but their shape is generally uneven and squared, often tapering towards the top. Menhirs are widely distributed across Europe, Africa, and Asia, but are most numerous in Western Europe; in particular in Brittany and on the British Isles. They originate from many different periods across pre-history, and were erected as part of a larger Megalithic culture that flourished in Europe and beyond.
The function of Menhirs has provoked more debate than practically any other issue in European prehistory. Over the centuries they have variously been thought to have been used by Druids for human sacrifice, or were territorial markers, elements of a complex ideological system, or early calendars. Until the nineteenth century, antiquarians did not have substantial knowledge of prehistory; and their only reference points were provided by Classical literature. The developments of radiocarbon dating and tree-ring calibration have done much to further human knowledge in this area.
The word menhir was adopted from French by 19th century archaeologists. It is a combination of two words found in the Breton language; men (stone), and hir (long). In Modern Welsh they are described as maen hir, or "long stone." In modern Breton, the word peulvan is used.

Description & History
Brittany stands out in the distribution of menhirs by virtue of both the density of monuments and the diversity of types. The largest surviving menhir is the world is located in Locmariaquer, Brittany, and is known as the Grand Menhir Brisé (Great Broken Menhir). Once nearly 20 meters high, today, it lies fractured into four pieces, but would have weighed near 330 tons when intact. It is placed second after the Western Stone in the Western Wall as the heaviest object moved by humans without powered machinery.
Alignments of menhirs are common, the most famous being the Carnac stones in Brittany, where more than 3000 individual menhirs are arranged in four groups, and arrayed in rows stretching across four kilometres. Each set is organised with the tallest stones at the western end, and shorter ones at the eastern end. Some end with a semicircular cromlech, but many have since fallen or been destroyed.

Partial list of menhirs

Drizzlecombe, Dartmoor, England
Goonhilly Downs, Cornwall, England
Drybridge, North Ayrshire, Scotland
Gigha Island, Kyle & Bute, Scotland
Callanish, Isle of Lewis, Scotland
Millport, Cumbrae, Firth of Clyde, Scotland United Kingdom

Carnac stones, Brittany
Filitosa, Corsica
Saint-Sulpice-de-Faleyrens, Gironde France

Lugnacco North West Italy. Italy

Sagres Portugal

Histria Neolithic 2.5 m high Romania

Björketorp Runestone, a menhir inscribed with runes.
Jelling stones Scandinavia

Grandson
Yverdon Switzerland

Le Roux, C.T. 1992. "The Art of Gavrinis Presented in its Armorican Context and in Comparison with Ireland." in Journal of the Royal Society of Antiquaries of Ireland vol. 122, pp79-108
Mohen, Jean-Pierre. 2000. Standing Stones. Stonehenge, Carnac and the World of Megaliths. London: Thames & Hudson. ISBN 0-500-30090-9 Sources
Obelix, a prominent character in the Asterix comic books by René Goscinny (stories) and Albert Uderzo (illustrations), is a menhir delivery man.

Notes

Statue menhir
Dolmens - megalithic tombs
Standing stone
Megalith
Menhir (Iron Age)