74 MEXICO AND CENTRAL AMERICA 
tures and paintings, while the outer room developed 
gradually into a portico. The outer wall was cut by 
doorways till only pier-like sections remained, and 
finally these piers were replaced by square or round 
columns. ‘The development of the Mayan temple may 
be traced through a thousand years of change and 
adjustment. 
Much attention was paid by Mayan builders to the 
question of stability which was accomplished directly 
by keeping the center of gravity of the principal masses 
within the supporting walls rather than by the use of 
binding stones. ‘The cross-section of a two-roomed 
temple of late date will illustrate how this was done. 
There are three principal masses, one over the front 
wall, one over the medial partition, and one over the 
back wall. The roof where these sections join is of no 
great thickness. The central mass is symmetrical and, 
if the mortar has the proper cohesiveness, very stable. 
For the front and back masses the projection of the 
upper or frieze zone tends to counterbalance the over- 
hang of half the vault. In the earlier temples the upper 
zone of the facade often slopes backward so that the 
balance is not so perfect. 
So far we have given brief space to the question of 
elevations. Taken vertically there are three parts to 
the Mayan building: first, the substructure or pyra- 
midal base; second, the structure proper; third, the 
superstructure. In the case of temples the structure 
proper is one story in height. Two and three stories 
are rather common in palaces, but the upper stories are 
in most cases built directly over a solid core and not 
over the rooms of the lower story. The upper stories, 
therefore, recede, so that the building presents a ter- 
raced or pyramidal profile. One building at Tikal is 
five stories in height, in three receding planes, the three 
