Ibbi-Sin, son of Shu-Sin, was king of Sumer and Akkad and last king of the Ur III dynasty, and reigned circa 2028 BC-2004 BC. During his reign, the Sumerian empire was attacked repeatedly by Amorites. As faith in Ibbi-Sin's leadership failed, Elam declared its independence and began to raid as well. Ibbi-Sin ordered fortifications built at the important cities of Ur and Nippur, but these efforts were not enough to stop the raids or keep the empire unified. Wikipedia
The definitive Wikipedia entry for Ibbi-Sin. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Ibbi-Sin