Isernia (anc. AEsemia), a town of southern Italy, in the province and 24 m. W. of the city of Campobasso, at the foot of the Apennines, and near the source of the Volturno; pop. about 7,500. It is surrounded by a modern wall, founded on the massive remains of an ancient one. In the middle is a fine fountain, with six rows of arches supported on columns of white marble; this, as well as the manufactories of the town, is fed by an ancient aqueduct hewn in the rock for a long distance and at a great depth. Isernia is the seat of a bishop, has cloth and earthenware manufactories and paper mills, and an extensive trade. Until 1780 it was crowded during the September fair with pilgrims to the shrine of Sts. Cosma and Damiano, who were supposed to have extraordinary healing powers, and to whom offerings were made of red wax models of the parts of the body affected by disease; these finally became so scandalous that the government suppressed the practice. In 1805 the town suffered severely from an earthquake.