The original surrounding moat was presumably symmetrical and located at the north of the rectangular rear-end part, although its north part is currently deformed thinly by filling in the moat from the outer side toward the embankment.
周濠に掛かる外堤は後円部北方にあり、また、北方の周濠は外側から埋め立てられて細く変形しており、本来の周濠は南北対称であったと思われる。