Archimedes Texts

174
for a Basement to them you must make a
Plinth half the Height of the Basement at the
Bottom. But nothing can be a greater Orna
ment either to Squares or the Meeting of seve
ral Streets, than Arches at the Entrance of the
Streets; an Arch being indeed nothing else but
a Gate standing continually open. I am of
Opinion, that the Invention of Arches were
owing to those that first enlarged the Bounds
of the Empire: For it was the ancient Custom
with such, as we are informed by Tacitus, to
enlarge the Pomoerium, or vacant Space left
next the City Walls, as we find particularly
that Claudius did. Now though they extend
ed the Limits of the City, yet they thought it
proper to preserve the old Gates, for several
Reasons, and particularly because they might
some Time or other happen to be a Safeguard
against the Irruption of an Enemy. Afterwards
as these Gates stood in the most conspicuous
Places, they adorned them with the Spoils
which they had won from their Enemies, and
the Ensigns of their Victories. To these Be
ginnings it was that Arches owed their Tro
phies, Inscriptions, Statues and Relieves. A
very proper Situation for an Arch is where a
Street joins into a Square, and especially in the
Royal Street, by which Name I understand the

most eminent in the City. An Arch, like a
Bridge, should have no less than three open
Passages: That in the Middle for the Soldiers
to return through in Triumph to pay their
Devotions to their paternal Gods, and the two
Side ones for the Matrons and Citizens to go
out to meet and welcome them Home. When
you build one of these Triumphal Arches, let
the Line of the Platform which runs length
ways with the Street be the Half of the Line
that goes cross the Street from Right to Left,
and the Length of this Cross-line should never
be less than fifty Cubits. This Kind of Struc
tures is very like that of a Bridge, only it never
consists of more than four Piers and three
Arches. Of the shortest Line of the Platform
which runs lengthways with the Street, leaves
one eighth Part towards the Square, and as
much behind on the other Side, for the Plat
forms of Columns to be erected against the
Piers. The other longer Line which crosses the
Street must also be divided into eight Parts,
two whereof must be given to the Aperture in
the Middle, and one to each Pier and to each
Side opening. The perpendicular Upright of
the Piers that support the middle Arch, to the
Spring of that Arch, must be two of the afore
said Parts and a Third; and the Piers of the
two Side Arches must bear the same Proporti
on to their respective Aperture. The Soffit of
the Arches must be persect Vaults. The
Crowns of the Piers beneath the Spring of the
Arch, may be made in Imitation of the Doric
Capital, only instead of the Ovolo and Abacus
they may have a projecting Cornice either Co
rinthian or Ionic, and beneath the Cornice by
Way of Gorgerine, a plain Freze, and below
that an Astragal and a Fillet like those at the
Top of the Shaft of a Column. All these Or
naments together should take up the ninth Part
of the Height of the Pier. This ninth Part
must be again subdivided into nine smaller Parts,
five whereof must be given to the Cornice,
three to the Freze, and one to the Astragal
and Fillet. The Architrave or Face of the
Arch that turns from Pier to Pier must never
be broader than the tenth Part of its Aperture,
nor narrower than the twelfth. The Columns
that are placed in Front against the Piers must
be regular and insulate; they must be so raised
that the Top of their Shafts may be equal to
the Top of the Arch, and their Length must
be equal to the Breadth of the middle Aper
ture. These Columns must have their Bases,
Plinths and Pedestals as also their Capitals,
either Corinthian or Composite together with
Architrave, Freze and Cornice, either Ionic or
Corinthian, according to the Proportions al
ready prescribed for those several Members.
Above these Columns must be a plain Wall,
half as high as the whole Substructure from
the lowest Basement to the Top of the Cornice,
and the Height of this additional Wall must
be divided into eleven Parts, one of which must
be given to a plain Cornice at the Top, with
out either Freze or Architrave, and one and an
Half to a Basement with a reversed Cymatium
which must take up one third of the Height of
that Basement. The Statues must be placed
directly over the Intablature of the Columns,
upon little Pedestals whose Height must be
equal to the Thickness of the Top of the Shast
of the Columns. The Height of the Statues
with their Pedestals must be eight of the eleven
Parts to which we divided the upper Wall. At
the Top of the whole Structure, especially to
wards the Square, must be placed larger Sta
tues, triumphal Cars, Animals and other Tro
phies. The Base for these to stand upon, must
be a Plinth three Times as high as the Cor
nice, which is immediately below it. These
larger Statues which we thus place uppermost,