circumvallation

plural circumvallations

1. A rampart or other defensive entrenchment that entirely encircles the position being defended.

   [...] and in a word, would intrench and fortify them round with as many circumvallations and breast-works, as my uncle Toby would a citadel.

   1761, Laurence Sterne, The Life & Opinions of Tristram Shandy, Gentleman, volume 3, Penguin, published 2003, page 201

   2 more examples

   The Saxon architect had exhausted his art in rendering the main keep defensible, and there was no other circumvallation than a rude barrier of palisades.

   1819, Walter Scott, Ivanhoe

   He just managed to finish her in time—the day before the date fixed for his breaking ground on a greater business still, the circumvallation of Mrs. Dunn.

   1901, Henry James, Flickerbridge

   Antonyms: contravallation