Al Ibrahimi Mosque in Hebron is the world’s oldest sacred building still in use today in a practically continuous manner. It is believed to hold the remains of God’s prophet Abraham, his wife Sarah, their son Isaac and grandson Jacob, and their wives Rebecca and Leah. The sanctity of the site has contributed to the cultural endurance of Hebron.
 
It has made the town renowned the world over, giving its name to other places around the world, in the United Kingdom and the United States. It is not certain when the site became sacred. History books do not cover its history much before the Roman era. It is not known when the burial site of the Patriarchs was defined and when its sanctity started to spread. Its sacred status could go back to several centuries BC, with an enormous historical gap remaining between Abraham’s time on earth in the 17th Century BC and the Roman era, i.e. a gap of more than a thousand years. No one can know what happened during that time, especially as the ruins shed no light on the events that took place there.
 
The current structure is composed of a large enclosure built around a double-chamber cave. There are doubts shrouding even the origin of the enclosure. The Roman historian Josephus (approx. 37 – 100 AD) had listed all structures built by King Herod (rexit: 37–4 BC). However, the site was not on his list and nothing in his writings linked the structure to Herod. Nevertheless, the enclosure’s architecture is undoubtedly Herodian. The structure features the use of large stone blocks the length of which can exceed many meters (7.5 m for the longest), with a height of over one meter (1.4 m for the tallest). A number of archeologists (such as Conder, Betzinger, Robinson, Warren and Heidet) even maintain that the enclosure was built long before Herod’s reign. It should be noted that, despite the structure’s scale and exceptional longevity – in excess of 2000 years, and despite the many powerful earthquakes experienced by the region, it has not lost it stability and has never sustained damage that required restoration. Its stones are finely hewn, with a 10-cm-wide margin surrounding each of them. The original enclosure is a 16m-high southeast-oriented roofless rectangular structure (59.28 m x 33.97 m). Walls are 2.68-meter thick. Each wall consists of two parts. The lower courses are made of normal large and tall stone blocks, while the upper part features a total of 48 protruding square columns (16 on each of the long walls and 8 on each of the short walls), as well as smaller recessed areas between them near the corners. These pilasters increase the structure’s strength and add to it an aesthetic touch that contrasts with the monotony of the lower section’s flat surface. On top of each wall, several clay-plastered courses were added at later times (probably under the Ottomans). This section of the wall was stripped during the last renovation effort and the edges of its stones were lined.
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For more details read "Old Hebron, The Charm of a Historical City and Architecture"