BEIRUT (AP) — The Old City wall of Syria's Raqqa that was the scene of intense fighting Tuesday in the battle against the Islamic State group was once a testament to the golden age of Islamic civilization, when the city on the banks of the Euphrates River was the capital of the famed caliph Harun al-Rashid.

The 1,300-year-old structure was breached by U.S-backed Syrian opposition forces trying to capture Raqqa who brought the fight closer to the heart of the IS-held city.

The Islamic State militants fortified their positions, booby-trapping the 2,500 meters (yards) long Old City wall — or the Rafiqah Wall — to protect their de facto capital.

The U.S. military said warplanes hit "two small portions" of the wall to allow allies from the Kurdish-led Syrian Democratic forces to push through.

The wall was built to protect Rafiqah, or "Companion" in Arabic — an 8th century garrison town built in the late 700s next to the city of Raqqa, on the road between Damascus and Baghdad. The town was modeled after Baghdad, then the newly built capital of the Abbassid Dynasty.

"The wall and the gate are major surviving monuments dating back to (Raqqa's) great's Islamic past," said Amr Al-Azm, a former Syrian antiquity official who currently teaches Middle Eastern history at Shawnee State University in Ohio.

The horseshoe-shaped town with its wall on the southern edge of Raqqa was chosen as the imperial residence of al-Rashid, the fifth Abassid Caliph well known for his "One Thousands and One Nights" tales.

Al-Rashid built a complex of palaces to the north and several canals and held horse races at Raqqa's hippodrome. The famous Raqqa pottery thrived to serve the new residents.

Al-Rashid's predecessor had ordered the building of a garrison town to protect the Abbasid dynasty from the Byzantine Empire. It was also at an important crossroads between the Euphrates and the Khabur River, which originates in Turkey.

Originally stretching 5,000 meters (yards), now only half of the wall remains. According to archeologists, the Old City had three gates and multiple defensive layers, including a wide moat, an outer wall and another inner one.

On Tuesday, U.S.-backed fighters entered through the Baghdad Gate, while others deployed around the area of Qasr al-Banat, or Girls' Palace, in the Old City, checking for land mines and IS militants.

Little is known about the Girls' Palace or when it was exactly built. UNESCO calls it "enigmatic" and archeologists differ over when it was built, some saying around the 12th century.

The Old City was destroyed by the attacking Mongols by mid-13th century and never regained its past glory. Most of the remaining wall and the gates have been extensively restored in modern day Syria, according to Al-Azm.