Fukuoka and Hakata used to be two distinct town, separated by Nakagwa River, in Edo Era, from 17th century to mid 19 th century. West side is Fukuoka, an administrative town, and east side is Hakata, a commercial town. There used to be a checkpoint gate in current Nakasu. People living in Hakata were required to hold permission to cross the river and enter Fukuoka. In 1889, two towns merged to become City of Fukuoka. In those days, Fukuoka and Hakata were widely treated as two distinct places. Kyushu Railway Company (later Japan National Railyways, and current JR) built the terminal station at current subway Gion area to name Hakata station, which is actually in Hakata. On the other hand, Nishitetsu Fukuoka Tenjin is in Fukuoka.
Gion Yamakasa is a festival of Hakata. Oiyama is all held in Hakata area, east side of Nakagawa River, except Day 13. Day 13's group performance (Shudan Yamamise) was started for the tourist promotion by the request of City Hall.
When you walk down the street in front of JR Hakata station or Watanabe Street in Tenjin, you may realise the buildings were as high as each other along the street. This is because the city is too close to the airport. Building height is regulated by the Airport Law. The tallest building is Hakata/Tenjin area is JR Hakata City.