Qal'a Najm is a fortification dating to the Islamic period situated on the right bank of the Euphrates river in Syria some kilometers east of the town of Manbij. The site of the fortification was strategic in the Roman and early Islamic periods because it overlooked a narrows on the Euphrates that was used as a crossing point on the route from Aleppo to Harran, thus linking northwestern Syria with northern Mesopotamia.
The ruins of the fortress take the form of a two story structure perched atop a rocky height. The chronology of these ruins is not entirely clear. Textual sources suggest that a bridge existed at the site since the time of the Umayyad caliphs and that the Umayyad bridge replaced an older, Roman structure. No remains of this bridge survive. In the twelfth century, Nur al-Din Zangi had the fortress restored, and several inscriptions on site credit Ayyubid Sultan al-Malik al-Zahir, son of Salah al-Din, with restorations undertaken between 1208-1215/605-612 AH.
Sourdel, D. “Ḳal'at Nad̲j̲m.” Encyclopaedia of Islam, Second Edition. Edited by P. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel, W.P. Heinrichs. Accessed May 9, 2017. http://dx.doi.org/10.1163/1573-3912_islam_SIM_3816.