Hostilities in this direction were precipitated by a rash and unsuccessful raid, from the opposite coast, upon Istakhr or Persepolis.[381] Alâ, Governor of Bahrein, who had distinguished himself in crushing the rebellion along the southern shore of the Persian Gulf, looked on with jealous eye at the conquests made in Irâc by Sád. Tempted by the closeness of the Persian shore, he set on foot an expedition to cross the narrow sea, and seize the district which lay opposite. This was done, not only without the permission of Omar, but against his known unwillingness to trust the treacherous element.[382] Success might have justified the project; but it fell out otherwise. The troops embarked with alacrity; and landing (it may have been) at Bushire, met for a time with no check in their advance upon Persepolis. [Sidenote: Meets with a check, but is relieved from Bussorah.]But before long they were drawn into a trap. Advancing confidently with their whole force in three columns, they had neglected to secure their base; and the Persians, coming behind, cut them off altogether from their ships. The Moslems, after a severe engagement, in which the leaders of two of the columns fell, were unable to disperse the gathering enemy; and, turning as a last resource towards Bussorah, found the road in that direction also barred. Messengers were hurried to Medîna, and Omar, highly incensed with Alâ for his foolhardiness, despatched an urgent summons to Otba to relieve from Bussorah the beleaguered army. A force of 12,000 men set out immediately; and forming, not without difficulty, a junction with Alâ, beat back the Persians, and then retired on Bussorah. The troops of Otba gained a great name in this affair, and the special thanks of Omar. [Sidenote: Campaign in Khuzistan. A.H. XVII. A.D. 638.]