, ▁during ▁the ▁era ▁of ▁Im am ▁Nas ir ▁bin ▁Mur sh id ▁al ▁Ya ' ar ub i . ▁R usta q ▁Fort , ▁built ▁four ▁centuries ▁prior ▁to ▁the ▁ 7 th ▁century ▁CE , ▁is ▁an ▁impos ing ▁structure ▁built ▁on ▁three ▁levels , ▁containing ▁separate ▁houses , ▁an ▁arm our y , ▁a ▁mos que ▁and ▁four ▁to wers . ▁The ▁tall est ▁tower ▁stands ▁over ▁ ▁high , ▁and ▁has ▁a ▁diameter ▁of ▁. ▁ ▁The ▁Haz m ▁Fort ▁is ▁an ▁out standing ▁example ▁of ▁O man i ▁Islam ic ▁architecture ▁and ▁was ▁built ▁in ▁ 1 7 1 1 ▁AD . ▁The ▁fort ' s ▁roof ▁is ▁built ▁on ▁columns , ▁and ▁contains ▁no ▁wooden ▁supports . ▁Its ▁walls ▁can ▁with stand ▁great ▁impact , ▁at ▁no ▁less ▁than ▁ ▁thick ▁at ▁any ▁point . ▁ ▁R usta q ▁is ▁an ▁area ▁of ▁he aling ▁warm ▁spr ings , ▁the ▁most ▁notable ▁being ▁' A in ▁al - K as af a . ▁Its ▁waters ▁runs ▁at ▁ ▁and ▁are ▁regarded ▁as ▁a ▁c ure ▁for ▁r he um at ism ▁and ▁skin ▁dise ases ▁due ▁to ▁its ▁sul ph ur ▁content . ▁ ▁There ▁are ▁three ▁popular ▁w ad is ▁to ▁visit : ▁W adi ▁B ani ▁Gh af ar , ▁W adi ▁al - Sa ht an ▁and ▁W adi ▁B ani ▁Auf . ▁In ▁addition , ▁the ▁mountains ▁are ▁p itted ▁with ▁c aves ▁such ▁as ▁Al ▁S ana q ha ▁C ave ▁with