Lewis & Short

ob-vallo, āvi, ātum, 1, v. a., to surround with a wall or rampart; to fortify, intrench.

  1. I. Lit.: urbem, Paul. ex Fest. s. v. ob, p. 179 Müll.
  2. * II. Trop.: locus omni ratione obvallatus. Cic. Agr. 2, 1, 3.