A handful of architects with formal training in classical architecture designed most of the distinctive white buildings surrounding Pioneer Courthouse Square. Development of the area-originally centered around McKim, Mead & White's famous Portland Hotel-was spurred on by the Lewis and Clark Exposition of 1905. By that time, steel framing had replaced cast-iron, allowing new buildings to be considerably taller than earlier structures. Facades were decorated with glazed terra-cotta tiles, a hard-baked clay shaped by hand into hollow blocks and pressed into plaster molds. Their terra-cotta faces give these buildings a soft white glow even on overcast days.