Painter Marc Chagall often told his old friends and Georgetown hosts, Mr. and Mrs. John U. Nef, that as a house present he would one day "make a mosaic for the garden." "I just thought it would be something 8 by 10 inches," says author and psychotherapist Evelyn Stefansson Nef, now widowed. "I never dreamed I'd have to build a 30-foot-high wall to hold it!"

The 10-by-17-foot mosaic that finally turned up depicts Orpheus, the winged Pegasus and other figures from Greek mythology across the top, but across the bottom tells of refugees who, like Chagall, had escaped Nazi-occupied France and found safe haven in America. "This was his way of saying 'Thank you for my life' to the United States," says Nef.

First painted in gouache by Chagall in 1969, the design was executed in France, under Chagall's direction, using bits of natural Carrara stone and Murano glass. With a complex network of architects, permits, contractors, cranes and bricklayers, Nef got the 10-panel mosaic installed in time for a dedication in the garden on November 1, 1971. Chagall, of course, was a house guest for the event, but this time left a less weighty thank-you: He brought a lithograph, but he also drew pictures in the front of all the Chagall books in the house.

The mural still dazzles in the walled garden beside the Nef town house, and though doorbell-ringers are definitely discouraged, students and scholars may make arrangements to view it. "I love people to see it," says Nef. "I feel it is a public trust."