According to the geographer Strabo, Hemeroskopeion was a small city founded by the Massaliot Greeks, colonists from Massalia, today's Marseille, together with two neighbouring settlements whose names have not survived at all. The perch that gave the city its name may have had a very practical purpose. One reading holds that its watchers scanned the water not for enemies but for fish, for the great shoals of tuna that migrated along this coast each year, whose arrival meant work and wealth for a settlement built around fishing. A watchtower, in other words, aimed at the sea's harvest rather than its dangers.

The city's defining landmark was sacred. On the promontory stood a sanctuary to Artemis of Ephesus, brought here from the Greeks' Massalian homeland, and the cape itself took the goddess's names, Artemisium, and later Dianium, after Diana, the Roman version of Artemis. Beyond its temple and its strategic height, the city drew wealth from iron mines nearby and from its role as a commercial and fishing emporium, a trading post where the goods and gods of the Greek Mediterranean met the Iberian shore. It was small, Strabo insists, but it mattered. The sanctuary's Ephesian roots tied this remote Iberian shore to one of the most famous temples of the ancient Greek world, a thread of shared worship stretching the length of the Mediterranean.

When Rome absorbed this coast, the Greek city became the Roman town of Dianium, named for the goddess on the cape, and it is from Dianium, worn down by two thousand years of speech, that the modern name Denia descends. For much of the twentieth century scholars toyed with a rival idea, that the name came from an Iberian settlement called Diniu, a theory propped up by certain ancient coins. The coins, it turned out, had been misread; they belonged to Tabaniu, a mint far away in the middle Ebro valley. The older explanation held: Denia is, at root, a city named for Diana.

The city steps into hard history in the first century BC, when both Strabo and Cicero mention it, Cicero noting that the rebel Roman general Quintus Sertorius used it as a naval base during Rome's civil wars. Under Roman rule the town held the status of a civitas stipendiaria, obliged to pay tribute and answerable to the governor of Hispania Citerior. Inscriptions name its decurions, the local councillors, and record a college of Sodales Augustales, freedmen devoted to the worship of the emperor. Burials show the city still alive through the third and early fourth centuries, and it likely passed under Byzantine control around the sixth. Each of these details is a fragment recovered from stone and text rather than from any certain ruin, which is what makes the city at once so well attested and so elusive.

For all these mentions, the ancient city itself remains elusive. Its exact site is still argued over, and some believe the Greek settlement grew from older Iberian establishments nearby, at Punta de Benimaquia or Pico del Aguila. So Hemeroskopeion keeps its final secret, a watchtower city whose own location has slipped out of view, known to us mostly through the words of writers who saw it when it still watched the sea. To stand in Denia today is, perhaps, to stand where Greeks once scanned the horizon for tuna and for gods. Perhaps the greatest of its ironies is this: a city named for the act of watching has itself become the thing that cannot quite be found.