In Shoho 2 (1645), Asano Naganao was sent to Ako to become the first feudal lord of the Asano family in Ako. He immediately began developing the Higashihama Salt Farm and preparing for the construction of a new castle. Ako Castle was completed in Kanbun 1 (1661), and it was composed of the Hon-maru (the innermost area containing the castle keep), the Ni-no-maru (an area forming a ring around the Hon-maru), and the San-no-maru (an enclosed area adjacent to the Ni-no-maru). Each of the three areas was completely surrounded by a stone wall. A special feature of the walls is that there are many corners, making it possible to see and attack invaders from multiple angles. While Ako Domain was under the rule of the Asano family, and subsequently the Nagai family and the Mori family, the vast tidelands to the east and west of this castle were developed into irihama salt farms, bringing tremendous profits that laid the foundation for the town of Ako. In Showa 46 (1971), the castle ruins were nationally designated as a Historic Site, and in Heisei 14 (2002) the gardens in the Hon-maru and Ni-no-maru, now referred to as “The Gardens of the Former Ako Castle” have been nationally designated as a Place of Scenic Beauty.