Lewis & Short

castellum, i, n. dim. [castrum],

  1. I. a castle, fort, citadel, fortress, stronghold, Sisenn. ap. Non. p. 514, 7; Caes. B. G. 2, 30; id. B. C. 3, 36; Cic. Phil. 5, 4, 9; id. Caecin. 7, 20; Sall. J. 54, 6; Nep. Milt. 2, 1; id. Alcib. 7, 4; Liv. 10, 46, 11; 21, 11, 10; Verg. A. 5, 440; Hor. Ep. 2, 2, 34 al.; also of a single bulwark, bastion, Caes. B. G. 1, 8; 2, 8; 7, 69; id. B. C. 3, 44; and poet. of a dwelling in an elevated position, Verg. G. 3, 475.
    1. B. In mechanics, a structure in which the water of an aqueduct is collected, to be distributed by pipes or channels in different directions, a reservoir, Vitr. 8, 6; Plin. 36, 15, 24, § 121; Front. Aquaed. 35; Dig. 19, 1, 17; 43, 20, 1; Inscr. Orell. 3203 al.
  2. II. Trop., shelter, stronghold, defence, refuge (cf. arx, I. B.): templum Castoris fuit arx civium perditorum … castellum forensis latrocinii, Cic. Pis. 5, 11: urbem philosophiae, mihi crede, proditis, dum castella defendis, id. Div. 2, 16, 37: tribunal Appii castellum omnium scelerum, Liv. 3, 57, 2.

Firmum, i, n.,

  1. I. a fortified sea-port of Picenum, now Fermo, Mel. 2, 4, 6; Vell. 1, 14, 8; Pompei. ap. Cic. Att. 8, 12, B. 1.
  2. II. Deriv.: Firmānus, a, um, adj., of or belonging to Firmum, Firmian: cohors, Liv. 44, 40: L. Tarutius Firmanus, of Firmum, Cic. Div. 2, 47, 98: audivi ex Gavio hoc Firmano, id. Att. 4, 8, b, 3: fratres, id. ib.
    Subst.: Firmāni, ōrum, m., the inhabitants of Firmum, Firmians, Cic. Phil. 7, 9, 23.
    Castellum Firmānōrum, the port of Firmum, regarded as a separate place, now Porto di Fermo, Plin. 3, 13, 18, § 111.