Wright's original concept was called an inverted "ziggurat", because it resembled the steep steps on the ziggurats built in ancient Mesopotamia. His design dispensed with the conventional approach to museum layout, in which visitors are led through a series of interconnected rooms and forced to retrace their steps when exiting. Wright's plan was for the museum guests to ride to the top of the building by elevator, to descend at a leisurely pace along the gentle slope of the continuous ramp, and to view the atrium of the building as the last work of art. The open rotunda afforded viewers the unique possibility of seeing several bays of work on different levels simultaneously and even to interact with guests on other levels. The spiral design recalled a nautilus shell, with continuous spaces flowing freely one into another.