The Barnes Foundation’s long and fitful quest to build a new art gallery for itself in Philadelphia marked a new chapter today with the announcement that its trustees, in a unanimous vote, selected architects Tod Williams and Billie Tsien. The Manhattan-based husband and wife team prevailed over a field of six semi-finalists in a two-stage competition.

Williams and Tsien have their work cut out for them. The Barnes has occupied a 10,000-square-foot, Classical-style structure designed by Paul Cret, set amid a 12-acre arboretum in suburban Merion, Pennsylvania, since 1922. Its namesake, Dr. Albert C. Barnes, specified that his collection of Impressionist paintings and other art works must remain intact and hung exactly as he specified. A judge ruled in 2004 that the Barnes could move as long as a new building maintained the scale, proportions, and hang of the original galleries.

After inviting some 30 firms to enter an RFQ in March, the Barnes selected Williams and Tsien, Tadao Ando, Diller Scofidio + Renfro, Kengo Kuma, Rafael Moneo, and Thom Mayne/Morphosis as semi-finalists. The architects made presentations in July and the trustees then made their selection last week. Martha Thorne, executive director of the Pritzker Architecture Prize, advised the foundation’s building committee and received assistance from Gary Hack, dean and Paley Professor at the School of Design at the University of Pennsylvania, and Suzanne Stephens, a deputy editor of RECORD.