dor-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
chamber is no wider than, and hence indistinguishable from the corridor,
the tomb becomes a long rectangular gallery, and answers to the French
_allee couverte_ in the strict sense. Fifthly, we come to the
_alignement_, in which a series of menhirs is arranged in open lines on
some definite system. We shall find a famous example of this at Morbihan
in Brittany. Sixthly, there is the cromlech (from _crom_, curve, and
_lec'h_, a stone), which consists of a number of menhirs arranged to
enclose a space, circular, elliptical or, in rare cases, rectangular.

These are the chief types of megalithic monument, but there are others
which, though clearly belonging to the same class of structure, show
special forms and are more complicated. They are in many cases
developments of one or more of the simple types, and will be treated
specially in their proper places. Such monuments are the _nuraghi_ of
Sardinia and the 'temples' of Malta and Gozo.

Finally, the rock-hewn sepulchre is often classed with the megalithic
monuments, and it is therefore frequently mentioned in the following
pages. This is justified by the fact that it generally occurs in
connection with megalithic structures. The exact relation in which it
stands to them will be fully discussed in the last chapter.

We have now to consider what may be called the architectural methods of
the megalithic builders, for although in dealing with such primitive
monuments it would perhaps be exaggeration to speak of a style, yet
there were certain principles which were as carefully and as invariably
observed as were in later days those of the Doric or the Gothic styles
in the countries where they took root.

The first and most important principle, that on which the whole of the
megalithic construction may be said to be based, is the use of the
orthostatic block, i.e. the block set up on its edge. It is clear that
in this way each block or slab is made to provide the maximum of wall
area at the expense of the thickness of the wall. Naturally, in
districts where the rock is of a slabby nature blocks of a more or less
uniform thickness lay ready to the builders' hand, and the appearance of
the structure was much more finished than it would be in places where
the rock had a less regular fracture or where shapel