Did you know that there once was a bridge that carried a canal across the Potomac River in Washington?

That question, and the details that follow, are prompted by a fascinating story by reporter Rick Allen in yesterday's paper. Allen related the uncovering of Lock No. 1 of the Alexandria Canal, which carried cargo boats from the lower end of the Chesapeake & Ohio Canal at Georgetown to the Alexandria waterfront. The lock is being restored to become the centerpiece of a major office complex.

Back to the canal bridge across the river. The ultimate skeleton of the Aqueduct Bridge is pictured above, in 1933, as it was being demolished. Key Bridge, then 10 years old, is to the right. In the Georgetown background is the Capital Transit Co. (later D.C. Transit) headquarters, which still stands.

As Rick Allen reported, the Alexandria Canal linked the rival ports of Georgetown and Alexandria from 1843 until 1886. The Aqueduct Bridge was built under congressional charter to let boats that arrived in Georgetown take their cargoes of grain and coal from Western Maryland to be loaded on seagoing ships at Alexandria.

South of the bridge, the canal was dug through land from Rosslyn, terminating with the lock unearthed at Alexandria. Some of the canal north of the Pentagon is now visible as the Boundary Channel between the District and Virginia.

During the Civil War, the aqueduct on the bridge was drained and a roadway substituted on the bottom of the trough. The boat channel was restored in 1868 and the bridge was decked over to allow a wagon road on its top.

In 1888 and again in 1908, the bridge was rebuilt, using steel beams that can be seen in the picture. A track for interurban electric trains from Virginia was laid on its deck, and passengers transferred to downtown-bound streetcars at the Georgetown car barn. Later, when Key Bridge was finished and Aqueduct Bridge closed, D.C. streetcars went to Rosslyn where the transfer was made.

It wasn't until 1962 that the Aqueduct Bridge piers were removed as eyesores and hazards to recreational boating.