Here is the passage from Josephus mentioning Helena’s palace: “Simon occupied the Upper City and the great wall as far at the Kidron (Valley); and a portion of the ancient wall where it bent back to the east from Siloam and descended until the palace of Monobazus (II), king of Adiabene beyond the Euphrates. He held also the spring and the Akra, that is the Lower City as far as the (palace) of Helena, mother of Monobazus” (Jewish War 5:252–253). Josephus uses Helena’s palace and that of her son Monobazus II to mark the northern line of Simon’s occupation of the Lower City. The palace of Monobazus II was located near the ancient wall that coursed (north)east from the Pool of Siloam along the eastern slopes of the City of David. The palace of Queen Helena is described together with “the spring” and “the Akra.” Routinely, when Josephus refers to “the spring” in Jerusalem, he has in mind the western opening at which the Gihon flows out from rocky escarpment on the slope of the City of David.
For Josephus the Greek term akra (height, hilltop, citadel) can refer to various designations in Jerusalem. In the passage concerning the palace of Helena, he qualifies the term to mean “the Lower City” which would include the area of the City of David. He is here demarking the northernmost point of the southern neighborhood held by Simon where it meets the Ophel under John’s control. These geographical markers suggest that Helena’s palace was in the Lower City between the Ophel and the western outlet for the Gihon spring where it begins its descent to the pool of Siloam.