Jorah Mormont: When the Doom claimed Valyria, the great freehold fractured into warring cities and upstart nations ripe for the taking. Out of the east swarmed the Dothraki, the horselords of the plains who feared only defeat and dragons, and now the dragons were all gone. Under the great Khal Temmo, they sacked and burned every town and city in their path. No army could stand against them, because the Dothraki do not stand. The horselords do not draw up battle lines or hide behind shield walls or layer themselves in armor. The Dothraki charge. Their blades are more scythe than sword, and better to cull the infantry ranks without breaking stride. Even their archers fire from horseback so that advancing or retreating, the arrows never cease. To the Dothraki, a man who does not ride is no man at all, without honor or pride.
When the city of Qohor realized Khal Temmo was coming, they strengthened their walls, doubled their own guards and hired two full companies of sellswords. The Dothraki were used to glorified farmers with spears; Qohor would show them a proper army, with armored and mounted cavalry to match the horde's own. As an afterthought, the city leaders sent an envoy to Astapor to buy Unsullied. The slavers had always claimed that the Unsullied were the great Ghiscari legions come again. Few cared. The dragon-burned ruins of Old Ghis were a stark reminder that the age of the foot-soldier was over. The envoy had his orders, however, and quickly bought three thousand Unsullied for the long march back, for Unsullied do not ride.
But while they marched, Khal Temmo arrived at Qohor. I can imagine how pleased the Khal was to finally face a challenge. By the end of the battle, crows and wolves feasted on what remained of Qohor's heavy horse. All the sellswords had fled. Qohor knew that the Dothraki would very soon break through the gates to rape, slave and burn at their pleasure. Yet the next day Khal Temmo woke to find before the gates three thousand eunuchs in formation, armed with only spears, shields and spiked helms. The Unsullied had slipped past the Khal's army in the night while the Dothraki feasted.
Khal Temmo had many times their number and could easily have flanked the small forces, but to the Dothraki, men on foot are made only to be ridden down. Eighteen times the horselords charged and eighteen times the Unsullied locked their shields, lowered their spears and held the line against twenty thousand Dothraki screamers. When the Khal's archers rained arrows on them, the Unsullied lifted their shields above their heads until the swarm passed; and then they held the line. In the end only six hundred Unsullied remained, but more than twelve thousand Dothraki lay dead - including Khal Temmo and all of his sons. The new Khal led the survivors past the city gates where one by one each man cut off his braid and threw it down before the feet of the Unsullied, defeated and shamed forever.
Since that day, the Unsullied fill the ranks of cities and households wealthy enough... or desperate enough. Sellswords fight for gold, knights for glory and Dothraki for blood. To a man, the Unsullied fight only to obey. With the right master over them, imagine how the forces of chaos would break against their shields: the conquerers, the madmen, the usurpers...
- Khal Temmo