Jerome : (Verse 30) And he said, 'You shall take these seven ewes from me, that they may be a witness for me that I have dug this well.' Therefore he called that place Beersheba, because both of them swore an oath there. Where this is read, Beersheba, in Hebrew it is called Beersheba. But there are two reasons why it is so named: either because Abimelech received seven lambs from the hand of Abraham, for seven are called Sheba, or because they swore there, for an oath is also called Sheba in the same way. But if we read this name above this cause, we shall know that it has been said by prolepsis: just as Bethel and Galgala, which were certainly called by different names until the time they were so named. But it should be noted both from the preceding and the present place, that Isaac was not born at the oak of Mamre, or in Aulon of Mamre, as it is stated in Hebrew: but in Gerar, where the town of Beersheba is still located today. This province, not long ago, was called Salutaris, after the division of the garrisons of Palestine. The Scripture is a witness of this matter, which says: And Abraham lived in the land of the Philistines (Gen. XXI, 34). — Hebrew Questions on Genesis