Tregaron (The Causeway): This Colonial Revival style estate is located on a landscaped, hilltop site above the Klingle Valley.

Tregaron (The Causeway), an estate designed in 1912 by Charles Adams Platt, is notable for its Colonial Revival design and landscaped grounds, as well as its former residents. Joseph Edward Davies and his wife, Post Cereal Company heiress and socialite Marjorie Merriweather Post, were the second occupants of the estate, beginning in 1941. While residing in the house, Davies made significant contributions to American history in the field of politics and government, during and after World War II. As an ambassador, Davies represented the U.S. to Belgium, Luxembourg, and, most importantly, the Soviet Union. His ties to the Soviet Union can be seen at the estate in the Russian-style dacha that he added in 1945.

The mansion is located at the very highest point of the hill, making it the focal point of the ensemble of buildings and grounds. Carefully planned vistas from the mansion overlook the city to the south and Cleveland Park to the north. The mansion is approached from Klingle Road over a stone causeway along a serpentine driveway, which affords a glimpse of the mansion crowning the hill and views into the informal landscaping at its base. At the crest of the hill, just prior to arrival at the main entrance of the mansion, the north vista opens out to the hilly meadow and heavily wooded area of mature trees below.

Today, the former estate composes both the Tregaron Conservancy and the Washington International School.

DC Inventory: January 5, 1979

National Register: June 28, 1990

Within Cleveland Park Historic District