I actually want to help you out here. This famous light cavalry you’re talking about from the Hungarians, it was actually reinforced by some more light cavalry – the Cumans.

I previously spoke about some Mongol sieges in a different post where I talk about the Mongol invasions West. In the first half I cover Batu’s campaigns against the Rus but also mention the subjugation of the other people such as the Volga Bulgars, the Alans and the Kipchak Turks or as we know them in the West, the Cumans. There was this sort of humanitarian crisis that caused 40,000 Cuman warriors and their families to leave the steppe and migrate into Hungary in the year 1239. The Cumans that did not migrate were now subjugated by Batu Khan; in fact, Batu considered the migrating Cumans to be property of his that just happened to run away.

The agreement between King Bela IV of Hungary and the Cumans was pretty straight forward: the Cuman chieftain Koten and his followers were allowed to come live in the plains of Hungary so long as he converted to Catholicism and pledged military support to Bela; on top of this, Bela would grant him the title ‘King of Cumania.” This was a precarious situation for the King of Hungary, on one hand, he had a new ally with experience fighting the Mongol; but on the other hand, this angered much of the nobility in Hungary who thought he was being power hungry. This also angered another group of people – the farmers. Hungary has a long tradition of farming, so you can imagine that a group of people such as the Cumans coming in and using the farmlands as pasture for their horses and cattle would anger many of the peasants.

A few years before (in 1237 to be exact), the Dominican Julian gave word to King Bela IV that the inhabitants of Great Hungary (meaning the old territories beyond the Ural) had been subjugated by these Mongols. Bela needed to hold on for just a little bit, he would deal with the angry nobles and peasants after this threat had gone, little did he know…that threat had arrived to his very doorstep.

I, the Khan, the representative of the Heavenly King, [the one] to whom He has given power over the earth, to raise up those who submit to me and to cast down those who resist – I wonder why, O king of Hungary, when I have now sent envoys to you on thirty occasions, you have sent none of them back to me; nor do you send me in return your own envoys or letter. I am aware that you are a wealthy and powerful monarch, that you have under you many soldiers, and that you have the sole rule over a great kingdom. Hence it is difficult for you to submit to me of your own volition; and yet it would be better for you, and healthier, were you to submit willingly. I have learned, moreover, that you keep the Cumans, my slaves, under your protection; and so I order that you do not keep them with you any longer and do not have me as an enemy on their account. For it is easier for them to escape than for you, since they are without houses and move about in their tents, and so may perhaps be able to escape. But as for you, who dwell in houses and have fortresses and cities – how will you evade my grasp?

In the year 1241 the Mongol army would head to Volhynia and divide their army, Hungary was the primary target; but although Poland was fragmented into feuding duchies, they posed a threat. Mongol scouts reported the relationship between the Hungarians and the Polish and also, that the Polish army would be able to pose a threat based on the way they would likely reinforce the Hungarians and so an army under Orda and Bajdar was sent to conduct a campaign in Poland.

With Poland taken care of, the Mongols were able to launch an attack that confused the nobles of Hungary. Batu and Subutai would go through the Verecke Pass in the Carpathian Mountains, whereas Kedan and Buri went though the Borgo Pass; there were also two other smaller divisions that were led by Bochek and Baghatur. The Mongols would harass the Hungarians making it difficult for Bela to mobilize.

On April 6th 1241, the armies would meet in the plains of Mohi (near the Sajo river). Some chroniclers claim that the Hungarian army was about 100,000 strong, which would have certainly made it larger than the Mongol army given that it had split before and during the campaign. The makeup of the Hungarian army were numerous armored knights while most of the army made up of these famous horse archers that you speak of, former Magyar nomads as well as the Cumans. The morale of Bela’s army was simply just low. First of all, their country had been ravaged, secondly, word of the defeat of Henry the Pious of Poland had reached them, third, the Knights weren’t too big of fans of Bela at the time and fourth, many realized that the Mongol army had Cumans in it…they began to think that these 40,000 Cuman refugees were infiltrators or even worse, that King Bela IV was conspiring with the enemy!

Subutai had gone south where he and his army had either found a bridge or created a small bridge at a narrow side of the river. Batu had sent an army north to find a shallow side of the river that they could cross from. This was because Bela had taken a defensive position on the bridge and as the skirmish began, it looked like the Christian army was getting the better of the Mongols. The problem here was that while the Hungarians were doing well on the bridge bunched up in a defensive position, well, they were bunched up in a defensive position! The army sent north and Subutai coming from the south ran up on Bela’s army and completely took them by surprise. The cavalry was unable to do anything from the harassment and Batu (in typical Mongol fashion) decided to add to the confusion by using siege engines in this open battle by launching anything his soldiers could find across the river. The Hungarian commanders did fantastic to rally their forces at the camp; however, Subutai would employee one of his preferred tactics of partial encirclement, he believed that fully encircling your enemy would make them feel like they had their backs against the wall and thus, they would fight back harder. But with partial encirclement, he gave his opponents the hope of escape, the reality was simply that they were being chased down by the horse archers. The results were devastating, somewhere between 50,000 to 70,000 soldiers in the Hungarian army had died. The Holy Roman Emperor, Frederick wrote about this stating:

The entire royal army of Hungary was destroyed.

King Bela IV was able to escape, but the population of Hungary was left at the mercy of Batu Khan’s troops, it is said that nearly half of the population was massacred or enslaved. The Mongols will do what the Mongols do best, they will raid the Balkans as far south as the Despotate of Epirus and some sources claim even as far as Constantinople.

The Mongols and the West by Peter Jackson

Subotai the Valiant by Richard A Gabriel

The Deed of the Hungarians: Epistle to the Sorrowful Lament upon the Destruction of the Kingdom of Hungary by the Tartars by an Anonymous Notary of King Bela and Master Roger