Given the historical background of the two old cities of Sarpol Zahab (old Hulwan) and Kermanshah (Qurmasin/Qarmisin in Arabic texts of the early Islamic Period), it can be claimed that one of the most important factors in the development and subsistence of the mentioned cities during the various historical periods has been the existence of two important rivers of Alvand (Alvan) and Qarasu. A study of different texts of the Islamic period indicates that the name of the old region and town of Hulwan has been adopted from the name of Alvan River. In the book Hudud al-álam (4th century, AH)
reference has been made to the exact location of Alvand River in relation to the city of Hulwan, and the name “Alvand” has been used in the same form until now. Regarding Qarasu River, it seems that this name replaced it old name in the Safavid period or a short time before that. The old name of Qarasu, like Alvand River, was probably similar to the name of a city in its vicinity. Accordingly, some options such as the ancient Korma River, Arazishoo River, and Gamasiab River have been discussed and studied in relation to the old name of Qarasu River. Based on the texts of the Islamic period and a number of scattered archeological proofs, it seems that the old city of Kermanshah was located in the south of Qarasu River under the Qajar texture of the present city.