Lewis & Short

prōpugnācŭlum, i, n. [propugno], a bulwark, tower, rampart, fortress, defence (class.).

  1. I. Lit.: pontes et propugnacula jungunt, Verg. A. 9, 170; Cic. Verr. 2, 5, 34, § 88: Siciliae, i. e. the fleet, id. ib. 2, 3, 80, § 186: solidati muri, propugnacula addita, Tac. H. 2, 19: moenium, id. ib. 3, 84: navium, i. e. ships furnished with towers, Hor. Epod. 1, 2; cf.: armatae classes imponunt sibi turrium propugnacula, Plin. 32, 1, 1, § 3: oppositum barbaris, Nep. Them. 6, 5: domus ut propugnacula habeat, Cic. Fam. 14, 18, 2: propugnacula aequoris, dams or dikes, Stat. S. 3, 3, 101: Cremona propugnaculum adversus Gallos, Tac. H. 3, 54.
  2. II. Trop., a bulwark, protection, defence (class.): lex Aelia et Fufia propugnacula tranquillitatis, Cic. Pis. 4, 9; cf. id. Verr. 2, 3, 16, § 40: tyrannidis propugnacula, Nep. Timol. 3, 3; Gell. 7, 3, 47; Liv. 34, 61.