covers possibly more than a thousand years.

What exactly is a megalithic monument? Strictly speaking, it is a
building made of very large stones. This definition would, of course,
include numbers of buildings of the present day and of the medieval and
classical periods, while many of the Egyptian pyramids and temples would
at once suggest themselves as excellent examples of this type of
building. The archæologist, however, uses the term in a much more
limited sense. He confines it to a series of tombs and buildings
constructed in Western Asia, in North Africa, and in certain parts of
Europe, towards the end of the neolithic period and during part of the
copper and bronze ages which followed it. The structures are usually,
though not quite invariably, made of large blocks of unworked or
slightly worked stone, and they conform to certain definite types. The
best known of these types are as follows: Firstly, the menhir, which is
a tall, rough pillar of stone with its base fixed into the earth.
Secondly, the trilithon, which consists of a pair of tall stones set at
a short distance apart supporting a third stone laid across the top.
Thirdly, the dolmen, which is a single slab of stone supported by
several others arranged in such a way as to enclose a space or chamber
beneath it. Some English writers apply the term cromlech to such a
structure, quite incorrectly. Both menhir and dolmen are Breton words,
these two types of megalithic monument being particularly frequent in
Brittany. Menhir is derived from the Breton _men_, a stone, and _hir_,
long; similarly dolmen is from _dol_, a table, and _men_, a stone. Some
archæologists also apply the word dolmen to rectangular chambers roofed
with more than one slab. We have carefully avoided this practice, always
classing such chambers as corridor-tombs of an elementary type.
Fourthly, we have the corridor-tomb (_Ganggrab_), which usually consists
of a chamber entered by a gallery or corridor. In cases where the