With the construction of the new terminal for the Pennsylvania Railroad (
PH143), the post office found a site across Market Street to connect its main sorting operations to the railroad that then carried the bulk of the nation's mail. The immense sorting facility was built as a part of the government response to the Great Depression. Its massive limestone walls frame interior courts that light the workrooms, while the public is served in a splendid corridor at the east end that is accented with symmetrically patterned marbles. The exterior has much of the Aztec modern in the pierced grilles above the entrances, suggesting the influence of Francisco Mujica's theory, advanced in his History of the Skyscraper (1929), that true American architecture should be rooted in the architecture of the Yucatan. Closed in 2008 and acquired by the University of Pennsylvania (
PH147) as part of its eastward expansion, it will house government and university offices.