From June 7 to July 15, 1099, the armies of the First Crusade laid siege to Jerusalem, then ruled by the Fatimid caliphate. According to two 12th-century accounts, the defenders dug a moat around the city as a protective measure, which took the Crusaders several attempts to cross. Archaeologists exploring the edges of the Old City have finished excavating the ditch, writes Amanda Borschel-Dan:
[The excavation’s] co-director Shimon Gibson laughingly said that contrary to popular imagination, the moat was most certainly not filled with water and patrolling crocodiles. Rather, it was a somewhat shallow ditch (thirteen-feet deep), he said, which would have been “an annoyance” to the invading Crusaders who could not stand their siege tower against the wall and gain a foothold into the city. In addition to the dry moat, other remnants of war include slingshots, arrowheads and pendant crosses. . . .
According to two chronicles, [the French commander] Raymond of Saint-Gilles offered his soldiers a gold dinar to fill the moat under the cover of night so a surprise siege tower could be placed next to the wall. While trying to break through, the Crusaders would have suffered showers of arrows . . . and cauldrons of boiling olive oil, said Gibson.
Despite the hardships [involved], the soldiers were successful in filling the ditch and the tower was built— but it was immediately burned down by the Fatimid defenders. A day later, other Crusader forces on the northern side of the city breached the walls. After their victory, the Crusaders spent another week slaughtering the city’s [Muslim and Jewish] inhabitants.
Read more on Times of Israel: https://www.timesofisrael.com/first-evidence-of-crusader-siege-from-july-15-1099-uncovered-at-old-city-walls/