The coastal city of Ashkelon was a frequent battleground during the Crusades (between the 11th and 15th centuries), changing hands between Muslims and Christians several times. An archaeological dig has revealed a siege ramp an army left behind has performed an unexpected role, saving the city from being swallowed up by the desert sands.
The walls ancient Canaanites built to protect one of their most important cities were breached many times over 5,000 years, but always rebuilt until 1270 CE when Sultan Baybars ordered the city destroyed. It's now a significant archaeological site, but Dr Rafael Lewis of the University of Haifa in Israel has spotted something others have missed, with considerable significance for the new city.
A village was established in the 15th century, inland of the old site, and has grown into a city that took its name from its famous predecessor. Praising the many fruits grown at Ashkelon, the 19th-century British visitor Claude Conder warned: “On the south the great waves of ever-encroaching sand have now surmounted the fortifications and swept over gardens once fruitful, threatening in time to make all one sandy desert, unless means can be found to arrest its progress.”
Looking at aerial photographs of the old and new cities, Dr Lewis noticed something was indeed blocking the encroaching sand dunes. The obstruction aligns perfectly with the ancient city's Jerusalem Gate, which Lewis considered an unlikely coincidence.
On investigating, Lewis realized a ridge 8-10 meters (26-33 feet) high and about 200 meters (650 feet) long running to the gate was stopping the sand dunes' advance. The ridge is obvious enough it appears on 19th-century maps, but if anyone before Lewis realized it wasn't a natural feature of the environment their observation wasn't recorded. The ridge is actually a ramp built by an army surrounding the city so they could bring siege engines from nearby high ground across a gully so they could storm the walls, Lewis revealed in a chapter in the book Crusading and Archeology.
Siege ramps were common in the area, despite the immense effort required to make them. Many were destroyed by the victors lest they be useful to future invaders, but a few were left behind by conquerors either supremely confident they would not be threatened themselves, or with no plans to keep the city.
What is different about Ashkelon's ramp is its subsequent effects. Without it the fields that cover the old city and extend to the north would not have remained some of the region's most fertile, Lewis believes. The city might never have been refounded. Lewis told IFLScience, “Medieval military formations...always reshape the lands around them to some extent,” but few would have been as influential as this.
It is known a siege ramp near the current location was built by King Baldwin III in 1153 to enable his successful takeover of the city, but Lewis believes the Crusaders must have demolished this afterward lest it be used against them. The surviving ramp would have been built for one of the subsequent battles, most likely to facilitate Baybar's victory. According to Lewis, previous Muslim rulers had tried to prevent Crusaders from establishing a coastal foothold by keeping small garrisons in many fortresses. Baybar learned from their failures and concentrated his forces at a few sites, destroying the remaining cities so they could not be used against him.
Lewis told IFLScience he's not an expert on preventing desertification, but understands “The best way to stabilize soil and keep away the desert is by vegetation”. Earth embankments sometimes help, but he doesn't think this one's success will see it replicated elsewhere instead of reafforestation.