The Army Corps of Engineers is going to be doing repairs to the Washington Aqueduct (underneath MacArthur Boulevard) during 2024 -- which so happens marks the 160th anniversary of its construction. 

The aqueduct's history is a fascinating story with the Palisades playing a small role, getting MacArthur Boulevard renamed from its original moniker, Conduit Road (for the 12-foot wide water tunnel under it).

This presentation tells the story through historical photos and maps to identify landmarks people have no doubt driven by without much of a thought. The entire 12-mile engineering feat (from Great Falls to the Dalecarlia Reservoir and then on two more miles to the Georgetown Reservoir) is now a National Landmark itself.