A little way along the coast is Silifke, classical Seleucia, a town on the River Göksu dominated by a castle which is part-Byzantine, part-Armenian. The curtain, reinforced by semi-circular towers, a feature of Armenian military architecture, is well preserved but the interior is a mass of rubble. From the ramparts you have a fine view over the Göksu delta, which is today a bird reserve. A few miles upstream, overlooking a gorge, stands a memorial stone, recording in Turkish and German that Frederick Barbarossa, the crusading Holy Roman Emperor, drowned while fording what was then called the Calycadnus on June 10, 1190.

Continuing westwards, the last of the great Crusader castles on Turkey's Mediterranean coast is Mamure Kalesi, near Anamur. It is an Armenian fortress with three baileys, protected on the landside by a moat in which turtles live. Its curtain and towers sport splendid crenellations, their preservation due to the fact that the castle was restored and garrisoned by the Ottomans. We were reminded of their presence when the recorded cry of the muezzin burst from the mosque they built within the walls.

After Jerusalem and Acre fell to Saladin, the Hospitallers based themselves briefly in Cyprus, where the keep of their castle at Kolossi, near Limassol, still stands, but then fell back to the Aegean coast and the Dodecanese.

At Bodrum, the ancient Halikarnassos, they built the fortress of St Peter on a peninsula at the centre of a large bay. It repelled a Turkish attack in 1480 and was strengthened in the early 16th century by the addition of a battery and ravelin overlooking the harbour, and a ditch and bastions on the northern, land side.

We had long wanted to see this castle but in the event were disappointed. On the west side, cruise boats with lofty masts crowd in on it, and from the sea the profile of its towers against the hills is spoilt by new building. 

The interior has been sacrificed to the needs of a museum of underwater archaeology. Old vaulting has disappeared, several of the towers were shut and coloured arrows indicating the shorter and longer routes round the castle gave it a regimented feel.

By contrast, the castle on the Greek island of Kos, an hour's boat ride away, was a delight. A double citadel built by the Hospitallers between 1450 and 1514, it has the charm of a classical site. Since ancient columns have been incorporated into the walls and litter the enceinte, that is hardly surprising. The fate of both Bodrum and Kos depended on Rhodes, which the Hospitallers had captured in 1310 and made into their new headquarters.

Two months ago, the town was packed with tourists, many of them off cruise ships, but we got away from the crowds by walking round the vast moat, whence you have an unrivalled view of the bastions, gateways and double line of walls which made Rhodes one of the most advanced fortifications in the world. The improvements carried out under later grand masters are commemorated by coats of arms on the ramparts bearing the hat of a cardinal; by a papal grant of 1489, the head of the order held that rank.