The Unisphere is built on a concrete foundation, which includes the piling ring that supported the Perisphere of the 1939 World's Fair. The marshy soil of Flushing Meadows needed special consideration during the original 1937 Perisphere construction. The Perisphere, and subsequently the Unisphere, employed a foundation of 528 pressure-creosoted Douglas fir piles of in length. Before construction of the Unisphere, three piles were tested for structural integrity and all were found to be sound throughout their entire length. Six hundred additional piles were built specifically for the Unisphere.