Lewis & Short

arx, arcis, f. [arx ab arcendo, quod is locus munitissimus rubis, a quo facillime possit hostis prohiberi, Varr. L. L. 5, § 151 Müll; cf. Serv. ad Verg. A. 1, 20; Isid. Orig. 15, 2, 32; Doed. Syn. IV. p. 428; v. arceo], a stronghold, castle, citadel, fortress, ἀκρόπολις; in Rome, the Capitolium.

  1. I.
    1. A. Lit.: arce et urbe orba sum, Enn. ap. Cic. Tusc. 3, 19, 44 (Trag. v. 114 Müll.): optumates, Corinthum quae arcem altam habetis, id. ap. ejusd. Fam. 7, 6: edicite per urbem ut omnes qui arcem astuque accolunt, cives, etc.; Att. ap. Non. p. 357, 14: Illa autem in arcem [hinc] abiit, Plaut. Bacch. 4, 8, 59; so id. Ps. 4, 6, 2: In arcem transcurso opus est, Ter. Hec. 3, 4, 17: Condere coeperunt urbīs arcemque locare, Lucr. 5, 1107: arcis servator, candidus anser, id. 4, 683: munire arcem, Cic. Pis. 34 fin.: cum Tarento amisso arcem tamen Livius retinuisset, id. de Or. 2, 67, 273: arx intra moenia in immanem altitudinem edita; Liv. 45, 28: arx Sion, Vulg. 2 Reg. 5, 7: arx Jerusalem, ib. 1 Macc. 13, 49: Romana, Liv. 1, 12: Capitolina, id. 6, 20; cf. id. 3, 18: Sabinus arcem Capitolii insedit mixto milite, Tac. H. 3, 69; Suet. Claud. 44 et saep. As the place on which auguries were received (cf. auguraculum): ut cum in arce augurium augures acturi essent, Cic. Off. 3, 16, 66; so Liv. 1, 18 and 24.
      Hence,
    2. B. Trop., defence, prolection, refuge, bulwark, etc.: Castoris templum fuit te consule arx civium perditorum, receptaculum veterum Catilinae militum, castellum forensis latrocinii, Cic. Pis. 5, 11: haec urbs, lux orbis terrarum atque arx omnium gentium, id. Cat. 4, 6; cf. id. Agr. 1, 6, 18: Africa arx omnium provinciarum, id. Lig. 7, 22: Stoicorum, id. Div. 1, 6, 10: arx finitimorum, Campani, Liv. 7, 29; 37, 18: tribunicium auxilium et provocationem, duas arces libertatis tuendae, id. 3, 45: arx ad aliquid faciendum, id. 28, 3: eam urbem pro arce habiturus Philippus adversus Graeciae civitates, id. 33, 14; Flor. 3, 6, 5: quasi arx aeternae dominationis, Tac. A. 14, 31.
    3. C. As the abode of tyrants, a poet. designation of tyranny (cf. Ascon. ad Cic. Div. in Caecil. 5), Claud. IV. Cons. Hon. 293 Heins.: cupidi arcium, Sen. Thyest. 342; cf. id. Contr. 4, 27: non dum attigit arcem, Juris et humani culmen, Luc. 7, 593 Corte; cf. id. 8, 490, and 4, 800; Tert. Apol. 4.
    4. D. Prov.: arcem facere e cloacā, to make a mountain of a mole-hill, Cic. Planc. 40.
  2. II. Since castles were generally on a height, meton., a height, summit, pinnacle, top, peak (usu. poet. and in Aug. and postAug. prose), lit. and trop.
    1. A. Lit.: summā locum sibi legit in arce, upon the extreme height, Ov. M. 1, 27; cf. id. ib. 12, 43.
      So,
      1. 2. In partic.
        1. a. Of mountains: Parnasi constitit arce, Ov. M. 1, 467: arce loci summā, id. ib. 11, 393: Rhipaeae arces, Verg. G. 1, 240: flērunt Rhodopeïae arces, id. ib. 4, 461: septemque unā sibi muro circumdedit arces, id. ib. 2, 535: primus inexpertas adiit Tirynthius arces, i. e. Alpes, Sil. 3, 496; cf. Drak. ad id. 15, 305; Val. Fl. 3, 565: impositum arce sublimi oppidum cernimus, Petr. 116; cf. id. 123, 205, and 209.
        2. b. Of houses built on an eminence, Petr. 121, 107, and 293.
        3. c. Of the citadel of heaven: quae pater ut summā vidit Saturnius arce, Ov. M. 1, 163: summam petit arduus arcem, id. ib. 2, 306: sideream mundi qui temperat arcem, id. Am. 3, 10, 21.
        4. d. Of the heavens themselves: aetheriae arces, Ov. Tr. 5, 3, 19: arces igneae, Hor. C. 3, 3, 10: caeli quibus adnuis arcem, Verg. A. 1, 250; cf. id. ib. 1, 259.
        5. e. Of temples erected on an eminence: dexterā sacras jaculatus arces, Hor. C. 1, 2, 3.
        6. f. Of the head: arx corporis, Sen. Oedip. 185; Claud. IV. Cons. Hon. 235.
    2. B. Trop., height, head, summit, etc. (rare): celsā mentis ab arce, Stat. S. 2, 2, 131: summae laudum arces, Sil. 13, 771; Sid. Carm. 2, 173: ubi Hannibal sit, ibi caput atque arcem totius belli esse, head and front, Liv. 28, 42: arx eloquentiae, Tac. Or. 10.