Rock Creek presents a formidable obstacle to easy travel between the eastern and western parts of the District, as bridging the valley required a considerable effort in each particular site. Though some bridges were built for military or infrastructure purposes, most were for the convenience of people moving between parts of the city, and were often financed by landowners who wanted to develop land.
The Aqueduct Bridge, now known as the P Street Bridge, was built to span the lower reach of Rock Creek and to support the aqueduct conduit that extended to downtown. In an unusual design, the steel arch doubles as a siphon, with the aqueduct's flow passing through the hollow tube among the main structural members. Though encased in concrete today, one can still see the original structure from beneath the present bridge.
The Q Street, or "Buffalo Bridge," was the result of yearslong advocacy by the population of the plateau north of Georgetown to have their own bridge to downtown. Built in 1914, its designers drew influence from the Ponte Maggiore on the Tronto River in Italy, with the buffaloes, sculpted by Phimister Proctor, adding a distinctly American motif.
The Military Road Bridge was built on the Civil War-era roadway constructed by the army for communication and supplies between the outlying fortresses protecting the capital. To save the army mules the effort of climbing up and down grade changes, the army built bridges across the intervening valleys. The current bridge occupies the site of one of these mule bridges.
An apocryphal story about Boulder Bridge records that the contractor mistook a line in the specifications about "man-size" stones to mean stones on the outline of the Vitruvian man-and not stones easily handled by one worker-thus the distinctive, rustic appearance of this bridge.