othona's location at the edge of the dengie peninsula was ideal for control of the estuaries of the rivers blackwater and colne, the latter leading to the important city of camulodunum (now colchester). the fort's shape was roughly trapezoidal, with rounded corners. the stone rampart was 4.2 metres thick, indicating a tall superstructure, and enclosed over . a single exterior ditch surrounded the site. although some of the roman building material was reused in the 7th century chapel of st peter-on-the-wall, enough of the rampart survived until the 17th century, when it was described by the local historian philemon holland as a "huge ruin". it has since been largely swallowed by the sea, leaving scant remains on view.