Internet History Sourcebooks Project
Fordham University: Medieval Sourcebook: Battle of the Yarmuk
This site from Fordham University provides an early writing describing the battle of Yarmuk, at which the Muslims defeated the Byzantine Emperor Heraclius and his army.
Islami City
Islami city.com: Seljuk Turks
This site provides a brief description of the origin and culture of the Seljuk Turks.