In November 1353, the Delhi Sultan Firuz Shah Tughluq launched an invasion of Bengal. His army occupied Pandua. Ilyas Shah and his forces retreated to the fortress of Ekdala. The Delhi Sultan laid siege to the fortress for two months. The Delhi Sultanate's forces then began withdrawing. Ilyas Shah began to pursue the Delhi army and reached as far as Varanasi. The Delhi army formidably fought back. Firuz Shah returned to Delhi in 1355. Ilyas Shah regained control of Bengal and his realm extended up to the Koshi River.