stylistic:tone, structural:summarization, quality:corruption
Construction

Soil conditions of the site – on the Potomac River floodplain – presented challenges, as did the varying elevations across the site, which ranged from 10 to 40 feet (3.0 to 12.2 m) above sea level. Two retaining walls were built to compensate for the elevation variations, and cast-in-place piles were used to deal with the soil conditions. Construction of the Pentagon was completed in approximately 16 months at a total cost of $83 million (equivalent to $ 1.33 billion in 2023). The building's approximate height is 77 ft (23 m), and each of the five sides is 921 ft (281 m) in length.