The description in Xenophon's Anabasis is unusually specific for ancient geographic writing. The promontory at Calpe, he noted, projects into the sea and ends in an abrupt precipice — a cliff that makes the seaward end essentially unassailable. The neck connecting this headland to the mainland is only about 400 feet wide, making the whole promontory something close to a natural fortress. The port lies to the west, sheltered by the rock above it. Fresh water springs from the ground near the beach. Timber grows in the hills immediately behind. Wood, water, a defensible site, a harbor: Xenophon ticked off the qualities of a viable settlement and concluded, explicitly, that this would be a good place to build a city. The site near the modern village of Kerpe, where ancient Calpe is generally located, still shows the coastal topography Xenophon described — the headland, the narrow neck, the sheltered bay to one side.

The men Xenophon led were not explorers or colonists by original intent. They were Greek mercenaries hired by the Persian prince Cyrus the Younger to help him seize the throne from his brother Artaxerxes II. Cyrus died in battle at Cunaxa in 401 BC, their Persian employers dissolved, and the Greeks found themselves stranded thousands of miles inside enemy territory without a patron or a plan. What followed — the long march north and west toward the Black Sea, fighting through hostile territory the entire way — became one of the most dramatic collective survival stories in antiquity. When they finally reached the sea at Trapezus (modern Trabzon), the men wept and embraced each other. Calpe came later, after they had turned west along the coast, still hungry and still fighting. By the time they reached the promontory, the debate about building a permanent settlement was real: some of the soldiers were genuinely considering whether to stop marching and start building. Xenophon himself favored the idea. He was outvoted.

Xenophon places Calpe about halfway between Byzantium and Heraclea Pontica — between the gateway to Europe and the main Greek city of the Pontic coast. That midpoint location gave the harbor a natural logic as a waystation for coastal traffic. Arrian, writing in the second century AD, placed Calpe 210 stadia from the mouth of the Psilis River. Solinus and Stephanus of Byzantium both noted the site. Its ancient name — Calpe or Calpas, shared with the river Calpas, modern Ilaflı Dere, that flows nearby — suggests the toponym predates the Greek presence. The river gave the place its name, or the place gave the river its name; in either case, the connection between water and settlement was the defining fact. Whatever city might have grown here did not; Calpe remained a waypoint rather than a destination, remembered mainly because Xenophon stopped there and wrote it down.

The site of ancient Calpe is today identified with the area near Kerpe, a small coastal settlement in Kocaeli Province on the Black Sea coast of Turkey. The modern village carries none of the weight of the ancient description — it is a quiet stretch of coastline, fishing boats, a beach, the forested hills of the Kocaeli Peninsula rising behind it. The dramatic promontory that Xenophon found so promising is still recognizable in the coastal geography, though the harbor has long since changed in use and character. Calpe exists now primarily as an archaeological and literary location rather than a living one: a place where scholars look at cliffs and measure necks of land against a two-thousand-year-old text, trying to confirm what they already believe — that the exhausted Greek soldiers stood exactly here, looked at exactly this view, and debated a future they ultimately walked away from.