Information about the design of East Building of NGA

In a moment of insight, I. M. Pei solved the problem of the site's irregular shape by dividing it into an isosceles triangle and a smaller right triangle. He later recalled, "I sketched a trapezoid on the back of an envelope. I drew a diagonal line across the trapezoid and produced two triangles. That was the beginning."

The early sketch, at left, shows the division of the site into two triangles. The West Building is represented by the lines to the left of the drawing, with the arrow suggesting its strong east-west axis.I. M. Pei. Early conceptual sketch for building plan, National Gallery of Art East Building, fall 1968.Crayon and graphite on tracing paper
In the quick study of the urban context for the building, below, Pei showed the profile and proportions of the East Building in relationship to the West Building and the U. S. Capitol.

Early in 1969, Pei's design was refined and elaborated to near-final form. The two triangles of the architect's original conception were pulled apart to create a slot that would emphasize the separateness of the two spaces: one for the museum's public functions and the other for its study center. Three towers were beginning to emerge at the corners of the isosceles triangle, balancing the east-west axis of the West Building.