ARCHITECTURE: 
times the pieys are even so broad, as to ad- 
mit of niches. The arch is either sur- 
rounded with rustic work, or with an ar- 
chivolt ; sometimes interrupted at the sum- 
mit with a key-stone in the form of a con- 
sole, or marsh, or some other appropriate, 
sculptured ornament. The archivolt rises 
sometimes from a plat band, or impost, 
placed on the top of the piers ; and at other 
times from an entablature, supported by 
columns on each side of the arch. In some 
instances, the arqhes of arcades are sup- 
ported entirely by single or coupled co- 
lumns, without the entablature ; as in the 
temple, of Faunus at Rome. This form is 
far from being agreeable to the eye ; it 
wants stability, as the columns would be 
incapable of resisting the lateral pressure of 
the arches, were they not placed within 
another walled inclosure, or in a circular 
colonade. In large arches the key-stones 
should never be omitted, and should be 
carried to the soffit of the architrave, where 
they will be useful in supporting the middle 
of the entablature, which otherwise would 
have too' great a bearing. 
When columns are detached, as in tire 
triumphal arches of Septimius Severus, and 
Constantine, at Rome, it becomes neces- 
sary to break the entablature, making its 
projection over the intercolumns, the same 
as if pilasters had been used instead of 
columns ; or so much as is just sufficient 
to relieve it from the naked of the wall. 
This is necessary in all intercolumns of great 
width, but should be. practised as iittle as 
possible, as it destroys the genuine use of 
the entablature. When columns are with- 
out pedestals, they should stand upon a 
plinth, in order to keep the bases dry and 
clean, and prevent them from being 
broken. 
Arcades should never be much more, nor 
much less, than double their breadth. The 
breadth of the pier should seldom exceed 
two-tliirds, nor be less than one-third of 
that of the arcade ; and the angular pier 
should have an addition of a third, or a 
half, as the nature of the design may re- 
quire. The impost should not be more than 
one-seventh, nor less than a ninth, of the 
breadth of the arch; and the archivolt not 
more than one-eighth, nor less than one- 
tenth, of that breadth. The breadth of 
the bottom of the key stone should be equal 
to that of the archivolt ; and its length not 
less than one and a half of its bottom 
breadth, nor more than double. In groined 
porticos, the thickness of the piers depends 
on the width of the portico, and the super- 
incumbent building; but with respect to 
the beauty of the building, it should not be: 
lgss than one quarter, nor more than one- 
third, of the breadth of the arcade. When 
the arcades form blank recesses, the backs 
of which are pierced with doors or win- 
dows, or recessed with niches, the recesses 
should be at least so deep, as to keep the 
most prominent parts of the dressings en- 
tirely within their surface. In the upper 
stories of the theatres and amphitheatres of 
the Romans, the arcades stood upon the 
podia, or inter-pedestals, of the columns ; 
perhaps as much for the purpose of pro- 
portioning the apertures, as to form a pro- 
per parapet for leaning over. 
Colonades. A colonade is a range of at- 
tached or insulated' columns, supporting an 
entablature. The interval between the co- 
lumns, measured by the inferior diameter of 
the column, is called the intercolumniation ; 
and the whole area between every two co- 
lumns is called an intercolumn. When the 
intercolumniation is one diameter and a 
half, it is called pycnostyle, or columns 
thick set ; when two diameters, systyieg 
when two and a quarter, custyle; when 
three, diastyle ; and when four, araeostyle,. 
or columns thin set. A colonade is also 
named according to the number of columns 
which support the entablature, or fasti- 
gium : when there are four columns, it is 
called tetrastyle ; when six, hexastyie ; when 
eight, octostyle ; and when ten, decastyle. 
The intercolumniations of the Doric order 
are regulated by the number of triglyphs, 
placing one over every intermediate co- 
lumn; when there is one triglyph over the 
interval, it is called monotriglyph; when 
there are two, it is called ditriglyph ; and 
so on, according to the progressive order of 
the Greek numerals. The intercolumnia- 
tion of the Grecian Doric is almost con-y 
stantlv the monotriglyph : from tins prac- 
tice there are only two deviations to he 
met with at Athens, the one in. the Doric 
Portico, and the other in the Propylasa ; 
but these intervals only belong to the mid- 
dle intercolumniations, which are both di- 
triglyph, and became necessary, on ac- 
count of their being opposite to the princi- 
pal entrances. As the character of the 
Grecian Doric is more massy and dignified 
than that of the Roman, the monotriglvphic 
succeeds best ; but in the Roman it is not 
so convenient, for the passage through 
the intercolumns would be too narrow, 
particularly in small buildings; the ditri- 
