The Islamist rebels who have been occupying the Crac des Chevaliers crusader castle near Homs probably didn’t spend much time contemplating the irony of it all.

The magnificent 12th century fortress, described as “the finest military fortification in the world”, was built by Christian warriors battling to crush Islam.

When I visited yesterday, the Islamists’ belongings – kettles, mattresses, cutlery, cassette tapes – were strewn across the floor of a vaulted church inside the fort which they seem to have used for living quarters. On a stone wall outside, someone had painted graffiti: “There Is No God but God and Allah is his Prophet. Sham Brigade.” Sham is the classical Arabic name for Syria.

Syrian government forces retook the castle on 20 March after an intense battle that destroyed the village below. As we drove up the winding road, it seemed that every building had been blown apart.

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An apartment block at the foot of the hill had been flattened, presumably by a government air raid. Other buildings had been holed by mortars which could have been fired by either side.

The inhabitants – Turkmens who reportedly supported the rebels while they controlled the castle – had fled. A sign saying “cocktails” flapped above what had presumably once been a bar for tourists.

I looked up from the carcass of a burnt out vehicle to the vast, looming turrets above.

A tattered Syrian flag fluttered at the entrance, where a small group of soldiers were cooking chicken over a grill. One told me that 2,000 rebel fighters had occupied the Crac. I suspect that’s an exaggeration, but it’s exactly the number of crusaders believed to have lived there in the 13th century when the castle was at its peak.

Lawrence of Arabia, who visited in 1909, called it “the most complete and most wholly admirable castle in the world”. It’s a Unesco world heritage site and archaeologists will be horrified at the damage modern warfare has wreaked.

The massive walls, some two metres thick, have been blasted by mortars and, in places, collapsed. We had to clamber over great piles of rubble to reach the church.

Ancient stonework has been pockmarked by bullets, and a bomb has gouged a metre deep crater in the ground between the outer and inner fortifications.

Footage from July last year shows Syrian government planes bombing the Crac in an attempt to dislodge the rebels, while other damage may have been done by the fighters.

As I picked my way through the debris in the church, I came across a child’s woollen booties lying on a carpet, while a small brightly coloured bedcover, patterned with cartoon animals, was tangled up with a pair of camouflage trousers – signs that the fighters had been living with their families and that they had fled in a hurry.

In a small enclave I found a pair of tennis shoes, a metal bowl, a cushion and a prayer mat. I looked up at the arrow slit in the wall and realised that in the exact spot from where a crusader archer must have fired his arrows 900 years ago, a sniper had taken up position just a couple of weeks back. He had covered the opening with twigs so no one could see him.

In the late 12th century an earthquake destroyed much of the Crac. They rebuilt the fortress, stronger and better. The crusaders, I thought, must have felt invincible behind those massive walls, dominating the valleys stretched out below. But the Mamluk Sultans besieged Crac des Chevaliers in 1271 and in the end the crusaders were overthrown.

I suspect the rebels felt invincible at one point too as they sniped at government soldiers from their castle on the hill. But they too were besieged and eventually defeated.

The Syrian soldiers I watched as they moved their bedsteads into the rooms where generation after generation of fighters have lived may have the upper hand in this war now. But history hasn’t come to an end in Syria. The damage to this magnificent fortress is testament to that. No one will control the Crac des Chevaliers forever.

Follow @lindseyhilsum on Twitter.