By means of a rigorous study of written primary sources coming from archives and from published information written by the missions' chroniclers, it was possible to reconstruct and reinterpret the architecture of the missionary churches in the Jesuit missions in Casanare, Meta and Orinoco in the Eastern Plains of the 'Nuevo Reino de Granada', including spatial characteristics of the layouts, the structural and construction systems, the materials used, and the objects and jewelry used as part of the decoration. Emphasis is laid on the importance of primary sources for the recovery of architectural heritage that no longer exists.