Tokyo is topographically separated into two areas, lowcity and uptown area. For example, Shibuya and Shinjuku are in the uptown area. On the other hand, Asakusa and Ginza are in the lowcity area. Speaking of popular obsrevatory decks, older one, Tokyo Tower is located in the uptown area. Newer one, Tokyo Sky Tree is in the low city area and nearby the Sumida River.     

People living in the lowcity area of Tokyo often suffered a great damage of flood. From around 1900, Tokyo expanded toward the lowland area or the east side. The government had to take measures by constructing the artificial waterway and a big watergate to stop flooding in the area. The mission was appointed to an experienced and competent engineer, named Akira Aoyama, who joined the construction work of the Panama Canal from 1904 to 1911. He conducted the difficult construction of them lasted for about 20 years until 1930 and accomplished it. Since then, the waterway and watergate have kept people living in the lowcity area safe. He is a great man.     

The red gate is an old one with no function which is now only a monument and recently has decided to become an important cultural property. Through the red gate, we see the blue gate a little faraway, which started to be used from 1982 as a new gate.