Chiyoda Ward in Tokyo was formed by the merger of Kanda Ward and Kojimachi Ward. The name Chiyoda Ward comes from the fact that Edo Castle was called Chiyoda Castle during the Edo period. The vast Imperial Palace sits at the center of the ward, occupying over 10% of the ward's total land area. The surrounding area is home to central buildings that run Japan, such as the National Diet, the courts, and the Prime Minister's Official Residence. Nagatacho in Chiyoda Ward is where many Diet-related people work. Marunouchi and Hibiya are also home to the headquarters of major companies. Since most of the ward is an office district, the daytime and evening populations vary significantly. Akihabara is a major tourist attraction, and it's the birthplace of AKB48.