Caliph
Umar (634–644) launched an offensive against the
Sassanid Persian Empire in 642, and by 651 the empire was destroyed. However, parts of
Khorasan were held by Sasanian loyalists helped by their
Hephthalite allies. In 651 the mission of conquering Khorasan was assigned to Ahnaf ibn Qais by
Abdullah ibn Aamir. Abdullah started to march in 650 from
Fars and took a short and less frequent route via
Rayy, while Ahnaf then marched north directly to
Merv, in present-day Turkmenistan. Later Ahnaf was sent by Abdullah to lead the vanguard of banu Tamim and 1000 Asawira through
Quhistan. The people of Tabasyin later revolted from the caliphate just to be reconquered by Ahnaf who now exacted heavier tool of tax. Ahnaf continued to advance. At first Herat agreed peace and pay Jizya. == Battle ==