Lewis & Short

circum-vallo, āvi, ātum, 1, v. a.,

  1. I. to surround with a wall, to circumvallate; in milit. lang., to blockade, invest, encompass in a hostile manner (class., esp. in the histt.): circumvallare loci natura prohibebat, Caes. B. G. 7, 17; 7, 11; id. B. C. 3, 43; Liv. 10, 35, 12 and 15; 28, 3, 4, and in part. perf. pass. Caes. B. G. 7, 44 fin.; Cic. Att. 9, 12, 1; Liv. 43, 19, 9.
    1. B. Trop.: tot res repente circumvallant, beset, beleaguer, Ter. Ad. 3, 2, 4.
  2. II. In gen., to surround, encompass: locum duobus sulcis, Col. 11, 3, 4; Claud. IV. Cons. Hon. 11: insula fluctisono circumvallata profundo, Sil. 12, 358.