At the mill complex that once filled this park, arched openings in buildings crossed raceways and defined windows and doors. Some of the arches remain intact, while many do not, and larger arches in the park survive with only a few stones left. Arch builders used temporary wooden supports called falsework or centering, then set bricks or stone blocks along the top from each end, installing the keystone section last. When the falsework was removed, the arch became self-supporting, and each piece worked in compression. The Broad Street Bridge has concrete arches faced with stone.