The Allen Center is a mixed-use skyscraper complex in Downtown Houston, Texas, United States. It consists of three buildings, One Allen Center (500 Dallas Street), Two Allen Center (1200 Smith Street), Three Allen Center (333 Clay Street). The complex has about of space. History The area that became the Allen Center was originally considered to be an eastern portion of the Fourth Ward. The opening of Interstate 45 in the 1950s separated the eastern portion from the rest of the Fourth Ward; that portion became the Allen Center and is now considered to be a part of Downtown Houston. TrizecHahn Properties acquired the Allen Center in 1996. Trizec defeated 16 other real estate companies so it could purchase the center for an amount reported by Tanya Rutledge of the Houston Business Journal as $270 million. When Trizec acquired the Allen Center in November 1996, the complex had a 76 percent occupancy rate. By 1997, Trizec had convinced several tenants of the Cullen Center, also owned by Trizec, to relocate to the Allen Center. Paul Layne, a vice president of the office division of Trizec, said that the shifting of tenants would lead to Allen Center having an occupancy rate of 92 percent in 1998. In 2001, when Enron collapsed, it vacated of space in the Allen Center and Cullen Center complexes in Downtown Houston. In 2010 Devon Energy was trying to sublease about of space that it occupied in the Allen Center complex. Hess Corporation announced it would vacate approximately of space in the complex when a new office tower in the east side of Downtown Houston opened. Major renovations to the property were completed in March 2021; these included new lobbies, bike storage, and a suite of rooms designated for breastfeeding mothers. One Allen Center One Allen Center is a 452 ft (138m) tall skyscraper. It was completed in 1972 and has 34 floors. It is the 31st tallest building in the city. One Allen Center employs a composite stub-girder steel frame floor system, originally developed in part by Joseph Colaco then of Ellisor Engineers Inc., currently of CBM Engineers, Inc. Macquarie Bank houses its Houston representative office in Suite 3100 of the building. Houston Public Library (HPL) maintains its Booklink facility there. Two Allen Center Two Allen Center was previously known as the Citicorp Building. Three Allen Center Three Allen Center is a 685-foot (209 m) tall skyscraper