Once the war broke out in earnest the Colonials were concerned that British warships would gain control of the Hudson River and separate New England from the rest of the colonies. Erskine designed a tetrahedron-shaped marine cheval-de-frise, a defensive barrier of pointed logs strung together abreast the river to prevent warships from sailing upriver. It was installed between Fort Washington on the northern end of Manhattan and Fort Lee, New Jersey in 1776.