72 MEXICO AND CENTRAL AMERICA 
Mayan area, was burned into lime. This was then 
slaked to make mortar and applied to a mass of broken 
limestone. ‘The facing stones were smoothed on the 
outside and left rough hewn and pointed on the inside. 
It is likely that these facing stones were held in place 
between forms and the lime, mortar and rubble filled in 
between. The resulting wall was essentially mono- 
lithic. The rooms of Mayan buildings are characteris- 
tically vaulted but the roof is not a true arch witha 
keystone. ‘The vault, like the walls, is a solid mass of 
concrete that grips the cut stone veneer and that must 
Osu 
CL 
ITO 
is 
Fig. 20. Groundplans of Yaxchilan Temples: (a) Structure 
2; (6) Struc > 25. 
42; (b) Structure 23 
