Lewis Short
(verb) : ob-vallo, āvi, ātum, 1
* To surround with a wall or rampart; to fortify, intrench.
* Lit.: urbem, Paul. ex Fest. s. v. ob, p. 179 Müll.—*
* Trop.: locus omni ratione obvallatus. Cic. Agr. 2, 1, 3.
Charlton T. Lewis, Charles Short, A Latin Dictionary