Large-scale commercial development began with Colony Square, the first mixed-use development in the Southeast, which was built between 1969 and 1973. The MARTA subway line opened in 1981. In the 1980s, many older properties were demolished, some remaining vacant for decades. High-density commercial and residential development took root in the north–south corridor along Peachtree and West Peachtree. The BellSouth Center (1982), now the AT&T Midtown Center, was long the landmark skyscraper in the area. However, commercial development escalated after 1987, when One Atlantic Center was completed.