The original town rose in the fifth century BCE, built by an Iberian people who traded briskly with the Greek and Phoenician merchants working the coast. In 219 BCE, Saguntum threw in its lot with Rome, and Hannibal answered by laying siege - eight months that ended in the city's destruction and gave Rome its pretext for the Second Punic War. What Carthage broke, Rome rebuilt. Later came the Visigoths, then Moorish rulers, then the armies of Jaime I of Aragon. Each left something in the stone. A modern visitor can read the whole sequence in a single afternoon's climb, and that is what makes the castle of Sagunto unusual. It is less a fortress than an archive, one civilization's wall resting on the ruins of another's.

On the slope below the castle sits the Teatro Romano, a Roman theatre cut straight into the hillside so that its tiers of stone seats look out over the rooftops and, beyond them, toward the sea. It is one of the oldest surviving theatres on the Iberian Peninsula, and restoration has pressed it back into service: on warm evenings, audiences again fill the ancient bowl for performances, their voices carrying on acoustics engineered before the birth of the printing press. Few places let you sit where a Roman spectator once sat and watch a living show from the same seat. Here the past is not behind glass. It is load-bearing.

Sagunto lives a double life. The historic centre gathers beneath the castle, its lanes threading past the old Jewish quarter and the Portalet de la Sang, the gate that once marked its entrance. A few miles away, the port district tells an entirely different story. In the early twentieth century, blast furnaces and steelworks drew thousands of workers to the shore, and Puerto de Sagunto swelled into an industrial town in its own right, complete with the fortified old anchorage of Grau Vell. Today the two halves share a name and little else - one medieval and inland, the other modern and maritime, joined by a bus line and a common history.

For all its ruins, Sagunto's summer draw is unabashedly modern. Thirteen kilometres of beach run north and south of the port - Playa del Puerto nearest the city, then L'Almardá, Corinto, and Malvarrosa stretching toward open country. From mid-June to mid-September the sands come staffed with lifeguards, first-aid posts, and showers. The closest beach is also the busiest; walk far enough north and the crowds thin to almost nothing, the developed strip giving way to dune and quiet, with a nudist section at the far end. Between a Carthaginian siege and an empty stretch of dunes, Sagunto covers remarkable ground.

Sagunto has not surrendered its hilltop to the tourists. Beneath the ruins it remains a working Valencian town, and it keeps the region's most theatrical tradition: the Falles, when neighbourhoods spend months building towering satirical figures only to set them alight in a single spring night, sacrificing a year of craft to the flames. The rhythm of the place is easy to catch. A single afternoon can carry you from the Iberian foundations on the crest, down through the medieval lanes of the old Jewish quarter, past the Roman theatre, and out to the port and its beaches - more than two thousand years compressed into a short walk and a bus ride. It is a town that keeps its past close without letting it turn the lights off on the present.