Constructed between 1900 and 1902 by Pennsylvania Railroad chief engineer William Henry Brown, the Rockville Bridge required the expertise of nearly 300 stone masons and is constructed from 220,000 tons of stone and 600,000 barrels of cement. Though iron bridges had become the standard replacement for earlier wood bridges that began to wear out around the turn of the century, Brown argued that lax maintenance rendered iron bridges a poor choice for the Pennsylvania Railroad’s busiest routes. Instead, Brown chose to construct costlier stone arch bridges that he believed would better withstand the heavy traffic that would utilize the bridge. The completed bridge at Rockville cost more than $975,000 and remains the longest bridge of its kind in the world. Considered a military target, it was placed under armed guard during both World Wars. The bridge has withstood two floods and continues to be used today.