The Mongols attacked the eastern side of Central Europe with five distinct armies. Two of them attacked through Poland in order to protect the flank from Polish cousins of Béla IV of Hungary, winning several victories. Most notably, they defeated the army of Duke Henry II the Pious of Silesia at Legnica. A southern army attacked Transylvania, defeated the voivod and crushed the Transylvanian armies. The main army led by Khan Batu and Subutai attacked Hungary through the fortified Verecke Pass and annihilated the army led by Denis Tomaj, the count palatine, on 12 March 1241, while the final army under Batu's brother Shiban marched in an arc north of the main force. Prior to the invasion, King Béla had personally supervised the construction of dense natural barriers along Hungary's eastern border, intending to slow the Mongol advance and obstruct their movement. However, the Mongols possessed specialized units who cleared the paths with great rapidity, removing the obstacles in just 3 days. Combined with the extreme speed of the Mongol advance, called "lightning" by a European observer, the Hungarians lacked time to properly group their forces.