impenetrable, invincible, unassailable, invulnerable, unbeatable, untouchable, unstoppable, unbreakable, unshakeable, assailable, indestructible, unshakable, formidable, watertight, fortified, immovable, unclimbable, undefeatable, insurmountable, inviolate, infallible, penetrable, impervious, fearsome, impermeable, bulletproof, ironclad, unmovable, unchallengeable, obdurate, porous, unconquerable, inviolable, immoveable, unbridgeable, bombproof, maginot line, imperious, insuperable, untroubled, resolute, unsurpassable, unscalable, unbendable, unthinkable, vaunted, impotent, crenellated, undefendable, undefended, sacrosanct, unvanquished, implacable, unflappable, nerveless, brittle, unassailed, airtight, unyielding, unflustered, peerless, unsusceptible, unattainable, imperturbable, irremovable, flawless, unquestioned, achilles heel, beatable, unbroken, unfathomable, vincible, inconceivable, sturdiest, untenable, faultless, moated, sandbagged, mortal, entrenched, stout, irresistable, irresistible, magnificent, foolproof, dominant, flimsy, indomitable, enviable, chinked, indispensable, unshaken, omnipotent, unchallenged, majestic, redoubtable, qui vive, exocet, unbending, mighty, immaculate, unbudging, sub, immune, lessees, national, operate, residing, sure, tell, above, acquisitions, adhering, anything, auto, bereft, boats, cease, circular, communiques, concur, contrary, inexpugnable, bastioned, inaccessible, stockaded, battlemented, palisaded, adamantine, castellated, girt, securest, demolished, intrenched, lofty, rugged, turreted

impregnably, invulnerable, maginot line

inexpugnable, inviolable, invulnerable, secure, strong, unassailable, unattackable, unconquerable