At least 10,000 men were involved in the first phase of the construction and more than 300,000 in the middle phase. When construction ended, the castle had 38 gates. The ramparts were almost high and the outer walls were high. Moats forming roughly concentric circles were dug for further protection. Some moats reached as far as Ichigaya and Yotsuya, and parts of the ramparts survive to this day. This area is bordered by either the sea or the Kanda River, allowing ships access.