In the spring of 1448, Ala-ud-Daulah Mirza was making preparations for the celebration of his son's circumcision ceremony. He had announced a general relief from taxes to all citizens of Herat when he heard the news of Ulugh Beg crossing the Amu Darya with 90,000 troops. He hastily made his way towards the Tarnab through the Sanjab Pass. The two forces met at Tarnab and after a brief engagement, Ulugh Beg decisively defeated Ala-ud-Daulah Mirza who fled towards Mashad and the towards Quchan in the protection of his brother Abul-Qasim Babur Mirza. Ulugh Beg followed up his victory by taking Herat and then Mashad. Goharshad and many Tarkhans left Herat before Ulugh Beg's arrival.