ZERETH-SHAHAR . A Reubenite town ( Joshua 13:19 ). Its site has not been identified.
Holman Bible Dictionary - Zereth-Shahar
(zee' rehth-sshay' hahr) Place name meaning, “splendor of the dawn.” The city located “on the hill of the  valley” was allotted to Reuben (Joshua 13:19 ). The site is perhaps modern Zarat near Machaerus on the eastern shore of the Dead Sea. Others suggest khirbet el-Libb seven miles south of Medeba or khirbet qurn el-Kibsh six miles northwest of Medeba.