Preparation for the campaign toward Europe required two years. Messengers went out in all directions to deliver the decision and distribute assignments. The system of post stations established by Genghis Khan was renewed and expanded by decision at the khuriltai of 1235; with a war on such a vast front, swift and reliable communication became more important than ever. Before the actual invasion, the Mongols sent in small squads to probe enemy defenses and to locate appropriate pasturelands and water sources for the Mongol animals. They identified valleys and plains that would best feed sheep or goats and those that would support cattle and horses. Where the natural grassland seemed inadequate, the Mongols opened up farmland for pasture by sending in small detachments of soldiers to burn villages and farm settlements in their future path. Without farmers to plow and plant the land, it reverted to grassland before the main Mongol army arrived.
The five-year European campaign marked the zenith of Mongol military ability, and almost everything went according to plan on the battlefield. The army for the invasion of Europe consisted of some fifty thousand Mongols and another one hundred thousand allies. Subodei embodied the accumulated knowledge of the old steppe hunter and warrior who had followed Genghis Khan closely and knew how he thought and fought. In addition, Mongke and Batu, the two smartest and most capable grandsons of Genghis Khan, helped to command the European war effort. By the start of the campaign, the Mongol army had absorbed the best of Chinese and Muslim technology and military knowledge, making it an incredible fighting force that probably surpassed the army commanded by Genghis Khan himself.
Subodei set the conquest of the Volga River, occupied by the Bulgars, as his initial objective. In 1236, the Year of the Monkey, the main army set out. They moved with a party of about two hundred scouts in front and with a rear guard of another two hundred warriors. Once they reached the Volga, the real invasion began. At this point, the Mongols enacted their unusual but, for them, tried-and-true strategy of dividing their army and invading on at least two fronts at once. In this way, the enemy could not tell which city or prince would be the main target. If any prince took his army from his home city to help another prince, then the other Mongol army could attack the undefended one. With such uncertainty and danger to his home base, every prince kept his army at home to guard his own territory, and none came to the aid of the others.
Subodei led his forces north up the Volga toward the homeland of the Bulgars, while Mongke, the eldest son of the deceased Tolui, led another force south toward the Kipchak Turks. Some of the Kipchak fled from him, but others agreed to join the Mongols in attacking the Russian cities. After the quick routing of the Volga Bulgars, the Mongols used their territory for the base camp and a reserve of millions of animals pastured on the steppes for hundreds of miles to the east. Some of the nomadic tribes already living in the eastern European plains joined with the Mongols, while others fled from them and spread fear and panic ahead of the invaders.
From the Volga, they began a three-year campaign across what would later become Russia and Ukraine. In their probes, they found the city-states and principalities still as divided and antagonistic toward one another as they had been when the Mongols invaded nearly two decades earlier. The Mongols followed the same protocols in every case. They began the campaign in each territory by sending official envoys to request the capital city to surrender, join the Mongol family, and become the vassals of the Great Khan. If they agreed, the envoy offered protection to the new vassals from their enemies and allowed them to keep their ruling family and their religion. In return for such protections, the people had to agree to commit tribute of 10 percent of all wealth and goods to the Mongols. Few cities took the offer.
The Mongols made the city of Riazan one of the first targets. The Chronicle of Novgorod for 1238 recorded that “Tartars came in countless numbers, like locusts.” First, small units of Mongol warriors divided to scourge the countryside. Each Mongol warrior seized a set number of civilians for the jobs ahead, such as digging fortifications, cutting trees, and hauling supplies. They then burned the villages and sent the remaining peasants scrambling toward safety within the city’s wooden walls. When the Mongol army finally reached the city, they sent, much to the consternation and horror of the people gathered inside, a woman ambassador to deliver their terms and demand surrender. Fearing that she was a witch, the city officials refused to admit her for any negotiation, and the Mongols prepared for attack.
Everything about the invading Mongols must have seemed horrifying to the Russians. “They have hard and robust breasts,” wrote an observer, “lean and pale faces, stiff high shoulders, and short distorted noses; their chins are sharp and prominent, the upper jaw low and deep, the teeth long and few, their eyebrows stretch from the hair to the nose, their eyes are black and restless, their countenances long and grim, their extremities bony and nervous, their legs thick but short below the knee.” When attacking, the Mongol warriors wore a light leather armor that was thick in the front but thin at the back so “that they might not be tempted to run away.” In battle, “they use darts, clubs, battle-axes, and swords . . . and fight bravely and unyieldingly, but their chief prerogative is their use of the bow.” If captured, “they never ask for mercy, and themselves never spare the vanquished.” It is their “intention and fixed purpose of reducing all the world under their dominion.”
Instead of attacking the walls of Riazan, the Mongols used their massive number of conscripted laborers in a project that confused and terrified the citizens even more. The workers cut down trees, hauled them to the Mongol lines outside the city, and rapidly began building a wall completely surrounding the already walled city. The Mongol wall formed a strong stockade that surrounded the city completely, sealed off the gates, and prevented the city’s defenders from sending out forays of troops to attack the Mongols or to destroy their siege machines. The wall was a wooden form of the traditional line, the nerge, used to enclose the animals in a group hunt. The Mongol wall cut off routes for reinforcements to arrive in the city or to bring food or supplies. Probably the most psychologically horrifying effect of the wall was that it sealed the people into their own city without hope of escape. Behind their wall, the Mongols remained out of range of the bows fired from the city wall, and they could set up their siege engines and other equipment without being seen.
From the safety of catwalks behind their own newly built wall, the Mongol warriors now looked down upon the city of Riazan exactly as generations of Mongol hunters had looked down at their tightly bunched hunting prey from behind the safety of their ropes strung from trees and hung with felt blankets. Already accustomed to attackers using catapults and battering rams, the city dwellers had not experienced the innovations in bombardment that the Mongols had developed into a new form of warfare. Their catapults rained down rocks, chunks of wood, flaming pots of naphtha, gunpowder, and other unknown substances. The Mongols used these as incendiaries to spread fires, but also as smoke bombs and to create terrible smells, which, at that time in Europe, were thought to be both acts of evil magic and the source of disease. In addition to shooting fire, the firelances could launch a small incendiary rocket or hurl exploding grenades over enemy walls. The mysterious devices provoked such terror that the victims later reported that the Mongols traveled not only with horses but with trained attack dragons as well.