Extensive fortifications recently discovered in the archaeological excavation in Silwan in East Jerusalem go back about 3,700 years, to the biblical period of the Patriarchs, revealing that Jerusalem at that time was significantly larger and stronger than previously believed.

According to the director of the excavation, Prof. Ronny Reich, the fortifications - the largest ever discovered in this area - were meant to create a protected link between the fortress-city in the area, known as the City of David, and the Siloam Spring. The fact that the spring was located outside the city walls was a major weakness in the city's ability to defend itself, Reich says.

"The construction of a protected passageway was a possible solution to the contradiction of the spring - the source of life for the inhabitants of the fortress in case of emergency - being located in the most inferior and vulnerable place in the area," Reich, of the University of Haifa, explained. In later periods, too, Jerusalem's rulers attempted to connect the spring to the city via walls and tunnels.

No fortifications of this size have ever before been discovered from the time of the First Temple, considered the zenith of Jerusalem's development in the biblical period. The next period of such massive construction would not be for another 1,700 years, during the time of King Herod in the Roman period.

The Canaanite walls the archaeologists discovered are about two meters apart, rise to a height of some eight meters in some places and are made of gigantic stones, three to four meters thick. About 24 meters have been exposed, but excavators say this is only one-third of their original length.

Excavation of the walls has been underway for about a year by the Israel Antiquities Authority, funded by Elad, the association that runs the nearby City of David antiquities site.

The walls have been dated by pottery to the period archaeologists call the Middle Bronze Age, better known as the "Period of the Patriarchs." At that time, Jerusalem was a kind of city-state - a fortress surrounded by farming plots. The massive nature of the fortifications has convinced archaeologists that the city was apparently larger and stronger than they had previously believed.

"To move such large stones, you need know-how and you need power," Reich says, "because a group of people doing the building needs a society to support them economically and a ruler to tell one group to work and the other group to support them."