The Romans were here. The Crusaders were here, and then the Muslims came. They've just discovered a bit of Beirut's Crusader castle.

Most of the other great coastal cities of Lebanon — Tripoli, Batroun, Jbeil (for which read Byblos) and Sidon — have their castles in various states of perfect preservation or decay, but the Ottomans and then the Lebanese commercial elite managed to destroy the great keep that guarded the port of Beirut, the first to use as a quarry for their walls, the latter out of greed.

After all, who wants a bloody great Crusader castle blocking the road to a thriving new port? So “zap” went Beirut's majestic castle. You can see it now only in the sketches of W H Bartlett in 1838 and of Samuel Green and — already in a pathetic state of disrepair — at the bottom of a British war department map of 1857.

Until, that is, Hans Curvers, one of the archaeologists who dug through the underworld of Beirut and who is now helping, along with urban planner Amira Solh, to |create a “heritage trail” — yes, aaagh, I hate the word “heritage” as much as any reader, of which more later — came across the very lowest wall of the castle. He shows it off proudly and, for a moment, I rather thought this Belgian-German archaeologist would like to claim ownership. The beautifully dressed Crusader stones — each with a delicately cut rim — are the base of a tower, the westernmost limit of the Crusader castle.

The Ottomans built their own fortress on top of it and part of their tower exists, too.

And, of course, you can find Crusader stones in the Ottoman fortification, just as you can find Roman columns embedded for support within the Crusader remains and — can we be surprised? — the 19th-century Brits, when they arrived in Beirut to defend the Druze from the Maronites (the French had already arrived to defend the Christians), built their own barracks on top of the rest.

In other words, each new military force, Roman, Omayad, Turkish, British, the Lebanese themselves, physically used their predecessor's history. Walking through the ruins with Hans, you can, far below the level of the forthcoming “trail” — see the relics of a Canaanite wall. In other words, the old city of Beirut is a giant historical club sandwich, the lower slice of stone “bread” being about 5,000 years old.

Like archive photographs, therefore, ancient cities are about memory, not so much about loss, but about witness. The Romans were here. The Crusaders were here and then the Muslims came. Indeed, one of the most beautiful mosques in Beirut, less than half a mile away, was a Crusader church, and when you go inside, it clearly was a Christian place of worship, complete with medieval arched windows and apse.

And when the French mandate authorities built their own shopping streets, they often used real Roman marble columns on either side of their doors to prettify their buildings. Then came the 1975-90 civil war to wreck the lot.

Most of mandate Beirut — though not the Ottoman bit, which was also trashed — has been restored. But the French street names have remained. So the titans of my Dad's First World War — Foch, Clemenceau, Allenby, Weygand — grace the walls.

Weygand has survived, but the hero of Verdun did not. When the British, Free French and Australians invaded Lebanon, they wouldn't tolerate “rue Maréchal Pétain” any more.

But I'm worried about the “heritage” bit, with its corny linguistic inheritance. There might be a site museum on a 5,000-year old Canaanite wall, but no one's going to dress up in Roman uniform or Crusader armour. It's true that there have been so many political assassinations in Beirut that one group of students has also cruelly suggested an “assassination trail” for tourists. I think “history trail” might be better. Even a “memory trail” — but which of Lebanon's religious communities will then try to lay claim to the largest memory?