In the pre-Islamic and post-Arab invasion periods, the Iranian frontiers were further to the northeast than at present, comprising the Oxus (Amu-Darya) and Iaxartes (Syr-Darya) rivers, and the Transoxiana (Mavara-ol-Nahr) region. Later, during the Qajar period, Iran's land area shrank considerably, and, based on the 1921 treaty, the present Sarakhs/Khazar border was eventually established (Fig. 2.1).