These structures are a significant example of local interpretation of constructive principles revealing the symbiotic process of indigenous masonry techniques and European applied geometry.
INDIGENOUS PEOPLE OF MEXICO BUILT THESE BUILDINGS
Upon the arrival of the Spanish in Mexico in the sixteenth century, it was necessary to construct new buildings that would accommodate the religious orders coming from Europe and scattering throughout the country. The Spanish had ambitious commissions to be accomplished in a new environment with a new set of conditions. The indigenous people of Mexico were the only labor force available and their skills were different from those of their Spanish counterparts. What did the Spanish master builders need to teach? How did the transference of technology happen? What did the indigenous people know and what did they need to learn?
These new methods of construction necessary to built ribbed vaults required a more skilled labor force. Mixtecs must have had an enormous impact in the construction processes and logistics. Their knowledge of quarry location, how to mine and carve stone, and the organization ability was essential to accomplish endeavors of such substantial magnitude.
To understand the underlying design principles of the Mixteca vaults, one should look to the Spanish manuscripts of the sixteenth century. The widely studied manuscripts of Alonso de Vandelvira (1580) and Hernan Ruiz (1560) identify the procedures that were performed at the time to define the geometry of vaults and their arches. These procedures began with simple line drawings. The first step was to set out a series of lines that would depict the vault on the horizontal projection, determining its overall proportion and ribs layout. The drawings of the manuscripts also contain the delineation of each arch within the vault on a vertical projection. Each segment of circumference was drawn overlapping on the same plane. Although the manuscripts depict a hypothetical vault, the purpose of the drawing was to define useful information to control the shape and size.
These line drawings were part of the technology brought to Mexico.
Different models were developed in Spain according to the different schools; the variants of the Spanish designs were multiple and usually very elaborate, creating intricate patterns. The stereotomy was a matter of more complex work, which required a more intricate process. The Spanish manuscripts did not come to the Americas in the sixteenth century but these documents reveal the common practices among the master builders of the time. These line drawings were part of the technology brought to Mexico. Looking at the three Mixtec vaults located in the towns of Coixtlahuaca, Teposcolula, and Yanhuitlán through the lenses of these manuscripts, one can discern the implications involved in the design process.
An important component in the construction process of a vault included the creation of scaffolding and centering.
Scaffolding and centering
Since scaffolding and centering were temporary structures, the information about how they were made is almost inexistent. Nevertheless, it is safe to assume that the formwork was made with wood, as the region had abundant forests. It is very likely that the experienced master builders from Spain guided the process of assembling this temporary structure, leaving the fabrication to the Mixtec carpenters. The scaffolding may have included a horizontal platform on which the layout of the vault was drawn at full scale. This drawing was similar to the drawings in the manuscripts including lines only. Once the scaffolding was completed, the vault construction began with the placement of bosses and keystones. Each of these stones was placed on a wood post. The length of the post was given by the drawings of the arches on the vertical projection, for which full-scale drawings on the ground were necessary. Carpenters developed templates to delineate arches. Once the path of the ribs and the points of intersection were located, the carpenters proceeded to manufacture centering to hold those pieces in their correct position within the vault. The completion of the arches was done constructing arches starting on the tas-de-charge. Voussoirs to form the web came after the ribs were securely placed, following the processes used on the Gothic vaults.