Paul Gendrop describes the beautiful portal arch at Labna as one of the true classics of the fully developed Puuc style. He writes:
"Conceived basically to join two groups of buildings now almost totally in ruins, this monumental arch embodies an architectonic concept unique to this region and entirely revolutionary within the Maya classical world. Actually, as we have seen in other regions of the Maya lowlands, the principle of the corbeled vault was conceived only as a system for roofing interior spaces...Here, on the other hand, the vault is used intentionally as a powerful formal resource penetrating the façade from one side to the other and opening plainly to the outside.
The appearance of this arch is particularly striking, with its lower walls slightly sloped, its gently concaved vault faces, its well accentuated upper ornamentation, and its simple but elegant outline, which is placed in relief by a well balanced and well contrasted decoration that changes radically from one façade to the other."
Paul Gendrop, Rio Bec, Chenes, and Puuc Styles in Maya Architecture, p. 190.