Herod the Great

Born around 73 BCE to Antipater of Idumea and Cypros of Nabataea, Herod came of age as Roman power subsumed the East. Backed by Mark Antony and later by Octavian, he was installed as king by the Senate in 40 BCE and fought his way into Jerusalem by 37. He ruled a tense, diverse kingdom with steel and spectacle. His public works—from fortresses like Masada to the Temple platform in Jerusalem—projected legitimacy in cut stone. But his most audacious act of statecraft occurred on the coast: to buy Judea a maritime future, he would build a harbor where there was none.

At Caesarea Maritima, Herod began in 22 BCE to engineer Sebastos, a deepwater port on an open shore. Roman crews floated timber caissons into place and sank them with volcanic-lime concrete—an opus caementicium mix that set in seawater, likely using pulvis from Campania shipped as cargo and ballast. Two immense moles, one stretching roughly half a kilometer, enclosed a basin on the order of 100,000 square meters. Divers could have felt the lime’s exothermic heat as concrete coursed into the forms; spectators on the dunes watched a gray, rammed stone rise where waves had broken the day before. The city behind it—gridded streets, theater, aqueduct—took shape because the moles held.

The project faced hard limits. The coast offered no natural lee; winter storms probed every joint; the treasury bled. Herod’s politics were blood-streaked—he executed rivals and even sons—and his piety, as seen by subjects, was suspect. Yet as a builder he was tireless, and his technical judgment was shrewd: only hydraulic concrete could grip that seabed. He hired the best Roman talent he could buy and bore the cost of trial and repair. His character combined grandiosity with calculation—a gambler who stacked the odds with engineering.

Sebastos changed the map. It pulled Mediterranean routes toward Judea, gave Rome a staging point on a once-hostile coast, and became the textbook example of large-scale marine concrete outside Italy. Later harbors took cues from its caissons and mixes; modern cores pulled from its moles still reveal the mineralogical signatures that Pliny would praise. In a story about turning ash and lime into a stone that the sea itself strengthens, Herod is the patron who proved the concept at imperial scale.