Lillebonne (Lat. Juliobona)a city of France, in the department of Seine-Inferieure, on the river Bolbec near its confluence with the Bec-quet, 19 m. E. of Havre; pop. in 1866, 5,049. It occupies a fine site in a beautiful valley, but has a dull sombre appearance, the most of its buildings being clumsy structures of wood, with long monotonous fronts. Almost all its inhabitants belong to the working class, and are employed in its numerous cotton and linen factories and tanneries. The parish church has a fine tower and spire, built in the 15th century. On a commanding site, overlooking the valley, are the ruins of a strong castle, built by William the Conqueror, who called here the great council of his barons to decide upon the conquest of England. The massive outer walls are still standing, but the hall has been demolished by its present owner. Near by is a tall round tower, with walls 13 ft. thick, isolated by a deep fosse, which is crossed by a drawbridge. It was built probably by the Harcourts, who owned the castle until the revolution. But Lillebonne is chiefly noted for its Roman remains.

Beneath the castle and partly cut out of the hill is the theatre, the best preserved example of its class in northern Europe. It measures 300 ft. across the chord of the arc, and around the whole runs a vaulted passage 625 ft. long. The walls are faced with ashlar masonry of calcareous tufa, and banded together at irregular intervals with courses of red tiles. Among other remains are a Roman bath, a Gallo-Roman house, and many sepulchral monuments; and statues in marble and bronze, sculptures, mosaics, and numerous utensils of gold, bronze, iron, ivory, and glass, have been found here. - According to Ptolemy, Juliobona was the chief town of the Ca-leti or Caletes, an Armoric tribe occupying what is now the Pays de Caux, Caux being a corruption of Caleti. In the decline of the Roman empire it was ravaged by the barbarians, and it did not again acquire any prominence until the time of William the Conqueror.