Reu/Rivu is also a Kashmiri surname. I do not know the etymology of the word as known in some other cases. For example, the Nehrus lived near a canal, Taklus had a bald forebear, Langu had a lame one and so forth. I also do not know the reason why my great-grandfather changed the surname. Or perhaps those before him were Reus but known under the common brahmin surname of Bhatta.
I would associate Bhatias with Bhatner, a fort in Hanumangarh, Rajasthan, and I think they were associated with the Sindhu-Sauvira kingdoms and Mahajanapadas. "Jayadratha was the king of Sindhus, Sauviras and Sivis." (Wikipedia) In Alexander's time, Multan was ruled by Mallis (it could even be 'mallisthan') who fought him bravely. Multan was important in that time and area as "Moolasthan" and had a huge Sun temple. It was later replaced by mosque which has been washed away in repeated floods in River Chenab.
This is how General Alexander Cunningham describes Multan in his "Ancient Geography of India", a captivating must read for anyone interested in Ancient Indian History (available on the internet):
"In the seventh century Hwen Thsang found a magnificent temple with a golden statue of the god most richly adorned, to which the kings of all parts of India sent offerings. Hence the place became commonly known amongst the early Arab conquerors as "The Golden Temple ;" and Masudi even affirms that el-Multan means "meadows of gold." Hwen Thsang calls it Meu-lo-san-pu-lo, which, according to M. Vivien de St. Martin, is a transcription of Mulasthanpura. that Multan was commanded by a citadel, which had four gates, and was surrounded by a ditch. .. I infer, therefore, that Muhammad Kasim may have captured Multan in the same way that Cyrus captured Babylon, by the diversion of the waters which flowed through the city into another channel. In this way he could have entered the city by the dry bed of the river, after which it is quite possible that the garrison of the citadel may have been forced to surrender from want of water. At the present day there are several wells in the fortress, but only one of them is said to be ancient; and one well would be quite insufficient for the supply even of a small garrison of 5000 men."
