Tregaron Estate is a twenty-acre Country Place Era house and garden located on the edge of Rock Creek Park. The land was acquired in the 1880s by Gardiner Greene Hubbard, founder of the National Geographic Society. Hubbard subsequently divided the property between his two daughters, one of whom married Alexander Graham Bell. The Bells never lived there, selling the land to James Parmelee, who named it “The Causeway.”
In 1912, Parmelee hired Charles Adams Platt to design a Beaux-Arts house and grounds. The layout of the property follows Platt’s typical schema of an entryway (in this case a causeway leading over a large stone bridge) bending toward an arrival court. Platt employed Ellen Shipman to design the gardens and surrounding woodlands. From the back terrace of the house, visitors encounter sweeping views: to the south, a meadow, woodland and a pond and cow pasture beyond; to the east, extensive woodland, traversed by bridle and woodland paths. In the 1930s, Ambassador Joseph Davies and his wife, Marjorie Merriweather Post, bought the estate and renamed it Tregaron. Post’s alterations included the addition of a Russian-style dacha in the western formal garden.
Today, the mansion and surrounding seven acres are owned by The Washington International School. In 2006, The Tregaron Conservancy was founded to restore the remaining 13 acres and ensure its perpetual preservation. In 1989, the National Register of Historic Places listed Tregaron Estate as Platt’s only surviving house in Washington, D.C., and as one of only three surviving Platt-Shipman collaborations nationally.