High Bridge was built as part of the original Croton Aqueduct project to bring water from the Westchester River to Manhattan. The bridge also incorporates a pedestrian walkway between the Bronx and Manhattan at 174th street. The bridge went into active service in 1848, making it the oldest extant bridge in New York City.
The bridge design was overseen by Aqueduct engineer John B. Jervis and James Renwick, Jr., who went on to oversee the construction of Manhattan's St. Patrick's Cathedral. The original design incorporated 15 circular masonry arches with a maximum length of 80 feet, giving the bridge a 114-foot clearance above mean high water.
The old Croton Aqueduct was made obsolete by a new series of tunnels and water flow was shut off on February 3, 1917 as part of security measures on the day the U.S. entered World War I. The Army Corps of Engineers wanted to demolish the bridge as an obstruction to river traffic, but a coalition of citizens groups pursuaded the Corps to replace five masonry arches with a steel arch in 1927.
There is some question as to the reason for and date of the bridge's closing. A posting on WiredNY...
I don't know where the rumor that the High Bridge was closed in the early 1970s after a fatal rock throwing incident, but it is pure nonsense, the result of lazy newspaper reporters who don't know how to, or don't care to, research. I have been attempting to ascertain exactly when it was closed, and have thus far been unable to, but it was definitely between 1958 and 1968, and most likely between 1958 and 1962.
I have conducted an exhaustive, extensive study of the New York Times Archives. On April 20, 1958, four youths threw bricks, sticks, and rocks onto the Circle Line as it passed under the High Bridge. Four people were injured, none seriously. When the New York Press ran a story on the High Bridge, someone wrote the next week, stating that he had moved to the Highbridge section of the Bronx in 1962, and the bridg had been closed even then. A New York Times reporter who followed the trail of the Croton Aqueduct in 1968 stated that the High Bridge was closed.
The Western approach to the bridge is considerably more forbidding. The old water tower has been lovingly cared for and the upper level of Highbridge Park (which includes a Robert Moses-era pool and recreation area) is still actively used. However, the stairway down to the bridge has not been maintained since the bridge was closed.