d as exhibiting the
maxima of simplicity in construction, and perfection in workmanship,--a
rare unison: for, in general, simple designs are rudely worked, and as
the builder perfects his execution, he complicates his plan. Nearly
all the arches of San Fermo are two-pieced.

[Illustration: Plate IV.
ARCH MASONRY.]

Sec. XIII. We have seen the construction with one and two pieces: _a_ and
_b_, Fig. 8, Plate IV., are the general types of the construction with
three pieces, uncusped and cusped; _c_ and _d_ with five pieces,
uncusped and cusped. Of these the three-pieced construction is of
enormous importance, and must detain us some time. The five-pieced is
the three-pieced with a joint added on each side, and is also of great
importance. The four-pieced, which is the two-pieced with added joints,
rarely occurs, and need not detain us.

Sec. XIV. It will be remembered that in first working out the principle
of the arch, we composed the arch of three pieces. Three is the smallest
number which can exhibit the real _principle_ of arch masonry, and it
may be considered as representative of all arches built on that
principle; the one and two-pieced arches being microscopic
Mont-Cenisian, mere caves in blocks of stone, or gaps between two rocks
leaning together.

But the three-pieced arch is properly representative of all; and the
larger and more complicated constructions are merely produced by keeping
the central piece for what is called a keystone, and putting additional
joints at the sides. Now so long as an arch is pure circular or pointed,
it does not matter how many joints or voussoirs you have, nor where the
joints are; nay, you may joint your keystone itself, and make it
two-pieced. But if the arch be of any bizarre form, especially ogee, the
joints must be in particular places, and the masonry simple, or it will
not be thoroughly good and secure; and the fine schools of the ogee arch
have only arisen in countries where it was the custom to build arches of
few pieces.

Sec. XV. The typical pure pointed arch of Venice is a five-pieced arch,
with its stones in three orders of magnitude, the longest being the
lowest, as at _b2_, Plate III. If the arch be very large, a fourth order
of magnitude is added, as at _a2_. The portals of the palaces of Venice
have one or other of these masonries, almost without exception. Now, as
one piece is added to make a larger door, one piece is taken away to
make a small