Battle at the Horns of Hazzat

After Daenerys Targaryen sacked Astapor, the city was left in the hands of a council of three former slaves. Cleon, one of them, stirred up the people with the claim that his fellow councilors wanted to hand power back to the Good Masters; on the strength of that accusation he had the rest of the council executed and proclaimed himself king. He restored slavery in the city and raised a new body of Unsullied to prop up his throne.

Cleon then sought an alliance with Meereen: he sent Lord Ghael to offer Daenerys a pact against Yunkai, one he would seal by casting off his wives and marrying her. Daenerys refused him again and again, since she needed her own armies inside Meereen to keep order, and she advised Cleon to do the same with his. Cleon ignored her and marched his Unsullied out to give battle.

Cleon's army was made up of freshly trained Unsullied, without the discipline of the ones Astapor had once fielded. Facing them, Yurkhaz zo Yunzak commanded a far more varied force: companies of slave soldiers under the direct command of the Wise Masters, two Iron Legions from New Ghis, and at least two mercenary companies hired for the occasion, the Windblown and the Company of the Cat.

At the Horns of Hazzat, Cleon found his army was no match for that combined force. He ordered a retreat and led his Unsullied back to shelter behind Astapor's walls.

The Yunkai'i did not let the advantage slip: they laid siege to Astapor, burned the fields around it and slaughtered what livestock remained, while inside the walls hunger began to take its toll on the Astapori.

Cleon did not live to see the siege's end: inside the besieged city, a man murdered him and proclaimed himself king in his place under the name Cleon the Second.

Some time later, Daenerys would admit she had let a chance slip by: "Cleon was the enemy of our enemy. Had I joined him at the Horns of Hazzat, together we might have crushed the Yunkai'i."