combat. They trained for virtually every possibility, so when it occurred, they could react accordingly. The Mongols also protected their ranking officers well. Their training and discipline allowed them to fight without the need for constant supervision or rallying, which often placed commanders in dangerous positions. Whenever possible, Mongol commanders found the highest ground available, from which they could make tactical decisions based on the best view of the battlefield as events unfolded. Furthermore, being on high ground allowed their forces to observe commands conveyed by flags more easily than if the ground were level. In addition, keeping the high command on high ground made them easier to defend from sudden attacks and invasions. Intelligence and planning The Mongols carefully scouted out and spied on their enemies in advance of any invasion. Prior to the invasion of Europe, Batu and Subutai sent spies for almost ten years into the heart of Europe, making maps of the old Roman roads, establishing trade routes, and determining the level of ability of each principality to resist invasion. They made well-educated guesses as to the willingness of each principality to aid the others, and their ability to resist alone or together. Also, when invading an area, the Mongols would do all that was necessary to completely conquer the town or cities. Some tactics involved diverting rivers from the city/town , closing supplies/resources to the city and waiting for its inhabitants to surrender, gathering civilians from the nearby areas to fill the front line for the city/town attack before scaling the wall, and pillaging the surrounding area and killing some of the people, then letting some survivors flee to the main city to report their losses to the main populace to weaken resistance, simultaneously draining the resources of the city with the sudden influx of refugees. Psychological warfare and deception The Mongols used psychological warfare extremely successfully in many of their battles, especially in terms of spreading terror and fear to towns and cities. They often offered an opportunity for the enemy to surrender and pay tribute, instead of having their city ransacked and destroyed. They knew that sedentary populations were not free to flee danger as were nomad populations, and that the destruction of their cities was the worst loss a sedentary population could experience. When cities accepted the offer, they were spared, but were required to support the conquering Mongol army with manpower,