To marauding pirates or would-be invaders, this fortified port, with rugged mountains on one side, sheer cliffs on the other and Lokrum island protecting the bay, must have appeared impregnable.

Even today, all that visitors can see as they arrive by boat is the formidable stone wall encircling the old town and harbour, hugging every contour of the land and flanked by towers, bastions and forts.

They are considered among the largest and best-preserved defensive walls in Europe, a remarkable testimony to the skill of the builders who created a structure strong enough to resist earthquakes, to the cooperation of the citizens, and, above all, to the astute diplomacy of a free city that managed to keep peace with the rival powers of the Ottoman Empire to the east and the Venetian Republic to the west.

For the people of Dubrovnik, the walled port remains a symbol of independence and prosperity.

The wall that shelters this jewel of the Adriatic stretches 2km (1.2 miles) in its entirety, climbing to the town’s highest point in the northwest corner, snaking along the cliff top, then dipping back down to the harbour. Rebuilt and altered many times, it reaches a height of 25m (82ft) in places and is up to 6m (20ft) thick, though less on the seaboard side, where limestone cliffs provided the first line of defence.

A walk along these ancient ramparts is breathtaking in every sense. Swept by a cool breeze or blazing in the summer heat, the outlook extends from rocky ridges on the hill above the city down to the Adriatic, from the meandering coast and glistening harbour to the old town with its jumble of red roofs sprinkled with spires and domes. Bells chime in the clear air and flagstones, polished by centuries of footsteps, shine like silver.

Construction of the current walls began in the 12th century and continued for the next 500 years. But why did this relatively small, southern European port need such hefty fortifications? As early as the 12th century, the autonomous city-state of Ragusa, as Dubrovnik was then known, found itself caught between a series of rival powers—the Byzantines and Venetians to the north and west and, later, the Ottomans to the east—as they vied to control the lucrative trading routes that crossed the Adriatic Sea.

With astute diplomacy, Ragusa managed to maintain its autonomy while gaining protection from the Byzantines and, later, from the Venetians. In 1440, Ragusa became a vassal state of the Ottomans but continued to operate as a free state, acting as a trading post between the Venetians and Ottomans. It was a time of great prosperity. The city’s fleet transported salt, wine, olive oil, dried fruit, leather and wool across the Mediterranean Sea and beyond. Aristocrats, ship-owners, merchants, bankers and an educated elite made the port their home.

When Constantinople fell to the Ottomans in 1453, followed by Bosnia in the 1460s, Dubrovnik decided the time had come to strengthen its defences. At the highest point of the ramparts, the circular Minceta Tower went up around an earlier fort, itself surrounded by thick walls and battlements.

Fort Bokar was designed to defend the Pila Gate, the main entrance on the land side of the town. Believed to be the oldest casemented fortress preserved in Europe, its massive cylindrical structure protrudes from the wall.

Guarding the port entrance in the southeast of the city, the mid-14th century St John Fortress was remodelled. At night, chains were stretched across the harbour entrance from the fortress to the Kase jetty, another protective barrier, to prevent access. To the east, the Revelin Fortress—erected in the 15th century and rebuilt in the 16th—could fend off any land approach.

Most forbidding of all is the St Lawrence Fortress (above), a triangular fort perched on a precipitous rock just outside the western wall and rising 37m (121ft) above the water. According to ancient documents, the Venetians had long
planned to take over this strategic spot, but Dubrovnik claimed it first and built the fort in just three months. A haunting place with terraces and arches, thick walls on the seaboard and two drawbridges, it is a popular setting for productions of Hamlet. Above the fortress gate is inscribed the motto so dear to the people of the city: "Freedom is not to be sold for all the gold in the world."

Four gates give access to the old town: two from the harbour—Ponte to the west of the Great Arsenal and the Fishmarket Gate to the east—and Ploca and Pila on the land side. Pila is an imposing structure with multiple doors, a moat,
a stone bridge and a wooden drawbridge. Above the gateway is a carving of St Blaise, patron saint of Dubrovnik.

The medieval thoroughfare known as Stradun leads from the harbour straight across the city, flanked on both sides by a grid of equally straight lanes that allowed messengers to move swiftly in all directions—from fort to fort, across town or down to the port.

Rebuilt after an earthquake in 1667, Stradun is an elegant, traffic-free esplanade paved with limestone. Both ends are marked by a lofty bell tower and a 15th-century fountain. The larger fountain, at the western end, has a massive dome surrounded by at least a dozen carved heads spouting fresh water piped from a spring more than 11km (7 miles) away. Several historical buildings grace Stradun and the adjacent Luza Square, including two palaces in Gothic-Renaissance style.

The Sponza Palace, where merchants, bankers and poets once met, houses the 17,000 volumes and manuscripts of the Dubrovnik Historical Archives. Baroque churches and monasteries stand proudly within the walls, while here an old granary, there a noble mansion with balcony and coat of arms, a stepped passageway, a tiny garden ablaze with sunflowers and pomegranates are tucked into side streets. Dark archways provide shade and in bustling squares, the scent of lavender rises from market stalls.

During the 19th century, Ragusa lost the freedom it cherished so highly—first to Napoleonic and then Austrian rule. A turbulent 20th century culminated in the Croatian War of Independence in the early 1990s, when forces of the Yugoslav People’s Army encircled and bombarded the city and its historic buildings for three months until a Croatian counterattack lifted the siege. Peace eventually returned and the damage was repaired.

Every hour on the hour, two bronze figures known as the "green men" strike the old bell in the clock tower on Luza Square, while in the glittering Renaissance palaces and along the fortifications looking out to sea, the free spirit of Dubrovnik lives on.

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