In March 2018 I made a trip to the ancient Mediterranean port of Acre in Northern Israel – Akka in Arabic, Akko in Hebrew  – as part of the research for writing my most recent book, Accursed Tower. I wanted to explore the place where the crusaders made their last stand in the Holy Land against an enormous Islamic army in 1291.

I thought I was fully prepared. I had read all the research literature I could get hold off. I had studied archaeologists’ reports and pinned their various attempts to map the medieval city onto my study wall. I wanted to get a sense of thirteenth century crusader Acre, its topography, quarters, principle buildings, the position taken up by the besieging Islamic army of the Mamluks. Above all I wanted to find out as much as I could about its defences. My unfolding book was full of the names of its towers and gates, descriptions of its moats and bridges. Where had the Accursed Tower been? The crucial Gate of St Anthony? The ominous Tower of Blood? And what did they look like?

I left a snowy England on the last day of February 2018 and stepped into brilliant Mediterranean sunlight. What confronted me was much more complicated than my months of book work had suggested. Old Acre, the ancient city, is a tiny place, but deceptive and as dense as Venice – winding streets, tiny squares, arches, dead ends, the domes of mosques, glimpses into courtyards – always ending somewhere by the sea. Above all it’s a Middle Eastern city, largely Palestinian, in which calls to prayer mingle with the sound of church bells.

I found the city walls impressive. Double-lined, with a deep ditch, they ring the peninsula of the old city from shore to shore. From the ramparts it’s possible to look out over the new town of Akko outside and imagine the defence, or back into the harbour.

The problem is that the walls I was standing on were constructed in the eighteenth century, probably from plundered medieval stone. They kept Napoleon at bay in a much later Mediterranean power struggle. I spent a little time with archaeologist Danny Syon of the Israel Antiquities Authority who disabused me of many of my more fanciful assumptions. Almost nothing remains of the famed defences. He showed me the one small stretch of crusader footing to a section of wall that’s now gone.

All the towers that the crusaders defended have vanished. Archaeological digs have discovered the remnants of some foundations, burnt in the final sacking of the city, but nothing exists above ground. I was little the wiser. Academic debate continues as to the size of the medieval city and the exact position of the walls.

Instead I found a much more complex scattering of crusader fragments built into later additions in a city whose street plan probably dates back to the long Arab presence. Everywhere Acre tantalises and perplexes, offers clues that one can’t quite read. My pleasantly cool Airbnb was vaulted with arches probably built during the crusader period.

This is a city – if we can call it one now – of immense antiquity and importance to the Middle East and the Mediterranean world. Everyone’s been here from the Bronze Age on: Alexander the Great, Julius Caesar, Cleopatra, Saladin, Richard the Lionheart, the Ottomans and Napoleon. The layers of history lie one on top of another in rich profusion. And it’s absolutely fascinating.

Everything in Acre leads down to the harbour, once one of the most important in the Mediterranean. Here goods were loaded and unloaded in an inner basin – archaeologists are still pondering exactly what was where. Fishing – the traditional activity of the local people – has declined, due largely to industrial pollution from nearby Haifa. (Perhaps nothing’s quite recent about this: all the sewage and the offal from butchers’ shops and the stinking effluent from tanneries poured into the medieval harbour, which was known as the Filthy Sea.)

Now the harbour’s main function seems to be providing speedboat thrill rides for tourists. The boats make tight turns, throwing out massive bow waves to the sound of blasting Arabic technopop. The passengers squeal in fear and delight. The last remnant of the medieval Tower of Flies that once enclosed the breakwater watches impassively.

One morning I walked out of Acre through modern suburbs to get a perspective from a prominent hill a few hundred metres to the south. Here the first inhabitants settled in the Bronze Age, and from this vantage point a succession of armies have conducted siege campaigns: Guy de Lusignan and Richard the Lionheart bottled up Saladin’s garrison for 683 days from 1189-91 before taking it back. Then in a final reversal of fortune the siege by the Mamluk Sultan Khalil a century later in 1291 that killed off the Holy Land crusades. I tried to imagine Khalil’s ceremonial red tent erected on the hill’s summit and his massive army ranged below, surrounding the Christian city in a great arc that stretched from shore to shore. Now the crest is surmounted by a later aspirant to Acre, the metal outline of Napoleon looking like a brandy advertisement.

I strolled along the fine sandy beach that stretches ten miles south to Haifa, as far as the mouth of the river Naiman that waters the fertile Acre plain and provided the city with food. The fine sand created a local industry in glass making from the time of the Phoenicians on.

Back in Acre I made a visit to the compound of the Knights of St John, the Hospitallers, which remains the most impressive remnant of its crusader days – and its touristic highlight – a warren of pillared halls, vaults and courtyards, displays of medieval pottery and graffiti, which give a sense of the enormous wealth that the military crusading orders possessed.

At the entrance to the compound there are collections of perfectly spherical limestone balls – the artillery that bombarded the city from giant Mamluk catapults. Some of these were quarried and transported from rock strata twelve miles away – harder than the city walls. The heaviest weigh up to 165 kilos.

I was also desperate to see what, if anything was left of the Templars’ Castle. Situated on the sea shore, it had been a formidable and magnificent complex, and the site of a dramatic last stand until its outer walls were undermined and collapsed. Instead I found just a shallow basin of sea, in which, when the water is still, you can discern the faint outline of foundations.

Across the street from the lost castle there’s a more imposing Templar memorial. A nondescript doorway leads down steps into the cool dark. For a small entrance fee you can descend into a subterranean world and gain a real sense of the Order’s wealth and power. The Templars’ tunnel runs for three hundred metres beneath the city. Constructed from extraordinarily well-cut stone, it’s an eerie place, dimly lit, curving away from you in an unknown direction. As the street noise fades, you hear, or think you can hear, ominous sounds: the mutter of voices, a cock crowing, the trickle of running water. Some of it is faked – an audio installation – but it’s a place where the distant past seems close. You emerge, surprised and blinking into brilliant sunlight close to the port. As with so many aspects of the city there’s uncertainty about the tunnel’s function. The most likely explanation is that it provided the Templars with secure access to and from the harbour, safe from quarrelling rival factions who controlled access above ground.

For ten days I poked and pried among Acre’s courtyards and alley ways. A day with local guide Andrew Abado helped me understand the medieval city more deeply. He took me into people’s cellars – deep underlayers – and picked out discernible features of medieval houses, gateways and warehouses, rebuilt or incorporated into other structures.

The pleasures of wandering in Acre seemed endless, despite its small size. I sat in mosque courtyards and in the caravanserais that accommodated Ottoman merchants, put my ear to the doors of churches where services were being conducted in Greek and in Arabic, stumbled on small squares – tiny breathing spaces in a dense urban space – where children played football, and experienced a lot of street art. The people of Acre seem to have a taste for creating murals and surrealist sculptures. The long covered market street is a souk for tourist souvenirs – toy boats, water pipes, evil eyes – as well as more useful things: fish, fruit and falafels.

The city’s soundscapes were vivid: squeals of kids on the speedboat rides, the somnolent cooing of pigeons, the more bloodcurdling shriek of a peacock that seemed to live on my roof, the echo of footfalls fading down alleys, the almost silent swoosh of electric bikes surprising the unwary from behind, the rustling of palm trees in the spring breeze.

At evening Acre reverts. The shop shutters in the market street close with a firm clang. The gawdy souvenir stalls vanish. The street turns to stone.

The theatre of twilight is entrancing. A Jewish shopkeeper unhooks the dresses hanging from his stall with a long pole. Backgammon games in a barber’s shop. A woman cooking in a kitchen. A tailor sewing by lamplight.  A man leads a gamely trotting pony that shies at the sparks from a welding torch as someone erects a metal structure over a gate. A cyclist swishes by, holding flowers in one hand with a snake round his neck.

At the day’s end the sea wall overlooking the vanished Templars’ castle becomes the place to promenade, meet friends and listen to the waves. A group of women in headscarves occupy a semi-circle of stone benches, chat and smoke waterpipes; a horse is hitched to a No Parking sign; the café is illuminated. Offshore, anchored merchant ships look like aircraft carriers. From here in late May 1291 the last desperate defenders of Acre scanned the horizon in vain for signs of rescue.

The speed boat thrills go on into the gathering night. Then sounds die away. My book closes where the Holy Land crusades stopped – at the sea’s edge: ‘After dark, just the slap of water, the fruit stalls still lit, the lighthouse and the moon.’

Roger Crowley is the author of The Accursed Tower.