Jaber

This Arab fortress is beautifully situated on a small island on the Euphrates River. Like most Arab fortresses it is situated on a hill and is surrounded by walls, towers and a ditch.
It is not known what was on this site before the Arabs built the fortress but it was held by the Arab tribe Banu Numeir, when the Seljuks took it. At the time of the first crusade it was probably annexed to Edessa's (today the city of Urfa in Turkey) territory. In 1144 it was taken by Zengi Atabeq of Aleppo, then it was handed down to his son Nur Al Din who constructed most of what we see today in 1168. It was handed down to Saladin but was destroyed by the Mongols in 1260. Although it was a bit rebuilt by the Mamelukes in the 14th century.
The most interesting parts of the Castle are the main entrance through a gate and the corridor that takes you up to the upper level of the wall. Also in the castle are a minaret made of brick which somewhat resembles the one in Al Raqqa. There has been quite a lot of restoration on the castle since the 1970's.
Nearby is the plain where the battle of Saffin took place between Caliph Ali (the fourth Caliph of the Rashedeen) and Moawiya Ibn Abi Sufian (the Umayyad Caliph). There is also the tomb of Suleiman Shah an early Ottoman sultan who drowned near here in the Euphrates. The tomb has now been moved upstream due to the widening of the Euphrates after the building of the Euphrates Dam.

http://www.syriagate.com/Syria/about/cities/Al_Raqqa/jaaber.htm