Bayezid’s second mistake was in putting his Tartar allies in the first line. He did this in accordance with the established Ottoman tactics, that the enemy be allowed to expend his strength upon the untrained rabble, and to reach the second line exhausted. But he had not taken into consideration the fact that these Tartars were kin to his enemy, and could easiest desert when placed in front.[625] A third mistake was in taking the offensive rather than waiting for Timur to attack;[626] for Bayezid had the advantage in being able to choose his position. From Nicopolis to Plevna, Tchataldja and Gallipoli, the Osmanlis have always shown their fighting qualities best in a defensive action. There was nothing the matter with Bayezid’s army. Like the empire he had been building, it was composed of all the Moslem and Christian elements of Asia Minor and the Balkan peninsula. With the exception of the Tartars, they were loyal to Bayezid, and had become accustomed to fighting together with a discipline and bravery fully equal to, if not superior to, that of Timur’s veteran warriors from central Asia. The right wing was under Stephen Lazarevitch, brother-in-law and faithful friend of Bayezid. In addition to Serbian horsemen, Stephen’s command contained the other European contingents, Moslem as well as Christian.[627] In the left wing were the troops of Anatolia, led by Soleiman Tchelebi, Bayezid’s eldest son. The emir himself was in the centre, surrounded by his janissaries and his three sons, Mustafa, Isa, and Musa. To Mohammed, whose reliability and judgement Bayezid esteemed second only to Soleiman’s among his sons, was entrusted the rear guard.[628] Elephants were used on both sides. Timur’s first line threw balls of Greek fire into the midst of the archers who were covering the Ottoman advance. The desertion of the Tartar auxiliaries, who formed a quarter or more of Bayezid’s total strength, decided the battle before the fighting really started.[629] When Bayezid saw that he could not prevent the Tartars from going over to Timur, he ordered the left wing to advance to the attack.