There are two architecturally notable buildings at the plaza. Directly west of the Aon Center and across from Millennium Park is One Prudential Plaza. Designed by Alfonzo Lanelli and completed in 1955, this limestone-and-ridged-aluminum structure was once the city's tallest building (barring the statue of Ceres atop the Board of Trade). At the time, it had the world's fastest elevators and an observation deck that became passé once some of the city's other behemoths were completed. Attached to One Prudential is its sibling Two Prudential Plaza, nicknamed "Two Pru," a towering glass-and-granite giant with an address of 180 North Stetson Avenue. Along with their neighbors they form a block-long business-oriented minicity. Two Prudential is the tallest reinforced concrete building in the city, and its blue detailing and beveled roof are instantly recognizable from afar.