work. [Footnote: The solitary exception at present known is an
Attic tomb built of crude bricks laid in lime-mortar] Consequently
in the walls of temples and other carefully constructed buildings
an elaborate system of bonding by means of clamps and dowels was
resorted to. Fig. 46 illustrates this and some other points. The
blocks of marble are seen to be perfectly rectangular and of
uniform length and height. Each end of every block is worked with
a slightly raised and well-smoothed border, for the purpose of
securing without unnecessary labor a perfectly accurate joint. The
shallow holes, III, III, in the upper surfaces are pry-holes,
which were of use in prying the blocks into position. The
adjustment having been made, contiguous blocks in the same course
were bonded to one another by clamps, I, I, embedded horizontally,
while the sliding of one course upon another was prevented by
upright dowels, II, II. Greek clamps and dowels were usually of
iron and they were fixed in their sockets by means of molten lead
run in. The form of the clamp differs at different periods. The
double-T shape shown in the illustration is characteristic of the
best age (cf. also Fig. 48).

Another important fact to be noted at the outset is the absence of
the arch from Greek architecture. It is reported by the Roman
philosopher, Seneca, that the principle of the arch was
"discovered" by the Greek philosopher, Democritus, who lived in
the latter half of the fifth century B. C. That he independently
discovered the arch as a practical possibility is most unlikely,
seeing that it had been used for ages in Egypt and Mesopotamia;
but it may be that he discussed, however imperfectly, the
mathematical theory of the subject. If so, it would seem likely
that he had practical illustrations about him; and this view