The +megalithic+ remains of Europe and Asia are far more important. They are very widely distributed, and consist in most cases of great blocks of stone arranged in rows, circles, or avenues, sometimes with huge lintels resting upon them. Upright stones without lintels are called _menhirs_; standing in pairs with lintels they are known as _dolmens_; the circles are called _cromlechs_. Some of the stones are of gigantic size, some roughly hewn into shape; others left as when quarried. Their age and purpose have been much discussed without reaching positive results. It is probable that, like the lake dwellings, they cover a long range of time, reaching from the dawn of recorded history some thousands of years back into the unknown past, and that they were erected by races which have disappeared before the migrations to which Europe owes her present populations. That most of them were in some way connected with the worship of these prehistoric peoples is generally admitted; but whether as temples, tombs, or memorials of historical or mythical events cannot, in all cases, be positively asserted. They were not dwellings or palaces, and very few were even enclosed buildings. They are imposing by the size and number of their immense stones, but show no sign of advanced art, or of conscious striving after beauty of design. The small number of “carved stones,” bearing singular ornamental patterns, symbolic or mystical rather than decorative in intention, really tends to prove this statement rather than to controvert it. It is not impossible that the dolmens were generally intended to be covered by mounds of earth. This would group them with the tumuli referred to below, and point to a sepulchral purpose in their erection. Some antiquaries, Fergusson among them, contend that many of the European circles and avenues were intended as battle-monuments or trophies. There are also +walls+ of great antiquity in various parts of Europe, intended for fortification; the most important of these in Greece and Italy will be referred to in later chapters. They belong to a more advanced art, some of them even deserving to be classed among works of archaic architecture. The +tumuli+, or burial mounds, which form so large a part of the prehistoric remains of both continents, are interesting to the architect only as revealing the prototypes of the pyramids of Egypt and the subterranean tombs of Mycenæ and other early Greek centres. The piling of huge cairns or commemorative heaps of stone is known from the Scriptures and other ancient writings to have been a custom of the greatest antiquity. The pyramids and the Mausoleum at Halicarnassus are the most imposing and elaborate outgrowths of this practice, of which the prehistoric tumuli are the simpler manifestations.