What is Idumaea?:
Idumea (Idumaea) is the Greek word for Edom that is used in the Septuagint. The name Edom comes from the Semitic root for red or ruddy and was probably created in reference to the red sandstone in the region. Almost nothing is known about ancient Edom. No inscriptions have been found and thus far only a few seals have been identified. This makes the Bible the only source of information on Edom and its not necessarily reliable.
Where is Idumea?:
Idumaeas borders changed dramatically, based on who was in control. Under David and Solomon it is thought to have been south and east of the Dead Sea, bordered on the north by Moab. Under Persian rule (539-332 BCE) it moved west of the Dead Sea and extended north to Hebron. Under the Maccabees the border moved even farther north. Under the Romans, the northern border moved south again.
Why is Idumea important?:
Idumea was conquered by Maccabean leader John Hyracanus (134-104 BCE) and all its inhabitants forcibly converted to Judaism. Their status as Jews was not, however, fully recognized by all pious Jews living in the north and as a consequence they were always treated as outsiders. Perhaps the most famous Idumean in the New Testament was Herod the Great, part of the Herodian dynasty that ruled over Palestine under the direction of Rome.