URBAN GENESIS AT CHACO: Case Study of the Origin of Civilizations. Chapters: 1 2 3 4 5 6
Figures 4.16 and 4.17. The expenditure of labor at Pueblo Bonito was
markedly dual in nature. On the one hand, the Chacoans took
extraordinary pains to preserve the original pueblo, eventually encasing
most of it with reinforcing walls. On the other hand, later builders did
not hesitate to demolish recent twelfth-century work in order to retain
the old (and very small) original structure as the focus of later
designs.
The initial form of Pueblo Bonito was a room-block in the shape of a multi-storied arc, built in the early 900s. The masonry technique used was crude: large slabs of sandstone were laid with thick beds of mortar between them, to compensate for the poor fit between the stones. Because the stones were not carefully worked, they were roughly lenticular in form. This created two problems: first of all, the major load of the wall was carried through stone-to-stone contact in a series of fulcrum-like points in the middle of the wall depth; secondly, the joints became largest where they were most vulnerable to weathering: at the outer surfaces. As a result these walls did not remain stable for long, perhaps one century. (Lekson 1984:23).
Around ad 1020, the Chacoans reinforced the original ninth-century core of Pueblo Bonito by building a new back wall to buttress the rear of the old structure(figure 4.17). It would have been easy to dismantle the old room-block and use the stone more effectively with the superior masonry techniques which the Chacoan masons developed in the eleventh century. Furthermore the hard, tabular sandstone which was used in the old core structure eventually became rare around the canyon; Flat stones became a limited resource by the end of the eleventh century, just as structural wood had always been in the canyon.
ABOVE: Central section of Pueblo Bonito. Remaining walls from 9th-century structure in foreground; 11th-century buttressing wall in background at left.
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