From A Wiki of Ice and Fire
|Sack of Astapor|
Art by Majoh
|Date || 299AL|
|Place || Astapor|
|Result || Sack of Astapor|
The Sack of Astapor took place in the year 299AL. Daenerys Targaryen, who had been travelling by ship, arrived at Astapor to buy an army of Unsullied. Sickened by the misery of the slave trade she saw, she acquired from the slave masters all the Unsullied available for sale in Astapor - 8,000, another 600 guarding the city and 5,000 boys still in training. In exchange for her ships, the trading goods on board and Drogon.
Other than the Unsullied, Astapor was poorly defended; its walls were old and crumbling, with no guards in the towers. Even a modest Dothraki Khalasar could probably have taken the city, but none has ever tried because of the Unsullied  and apparently, no one thought it was a bad idea to turn control of all of their best soldiers to an ambitious buyer such as the desperate queen inside their walls.
The exchange took place the next morning, at the 'Plaza of Punishment'. Having closed the deal, receiving the harpy's fingers, a nine lashed whip that symbolizes her ownership of the Unsullied, she betrayed the terms of the deal and unleashed her dragons on the masters and the few remaining soldiers in the plaza, ordering the Unsullied to kill the remaining slave-masters of the city and freeing all of the slaves.
Before leaving to Yunkai Daenerys left a council of three men, a healer, a scholar and a priest to rule. They were later deposed by Cleon, a former butcher, who led the people to believe that the three intended to return the Good Masters to their positions of power. Naming himself King after having the council executed, Cleon had all the highborn boys seized to begin training new Unsullied. Each pyramid within Astapor is now an armed camp and the dead lie in the streets and the markets of devoid of food and slaves to purchase.
References and Notes