Никита Хониат
According to Niketas Choniates, a Byzantine historian, in the day of the battle Tsar Kaloyan chose the place of the ambush in the following manner: "After which Yoan and his army hid in the ravines, entered the precipice and through those steep places crept to the highlands, making sure their opponents did not notice they were there". In other scriptures, it reads "...and hid in the narrows in the shadowy forests".