JESI (anc. Aesis)  , a town and episcopal see of the Marches, Italy, in the province of Ancona, from which it is 17 M . W. by S. by rail, 318 ft. above sea-level . Pop . (19ot), 23,285 . The place took its ancient name from the river Aesis (mod . Esino), upon the left bank of which it lies . It still retains its picturesque medieval town walls . The Palazzo del Comune is a fine, simple, early Renaissance building (1487–1503) by Francesco di Giorgio Martini; the walls are of brick and the window and door-frames of stone, with severely restrained ornamentation . The court-yard with its loggie was built by Andrea Sansovino in 1519 . The library contains some good pictures by Lorenzo Lotto . The castle was built by Baccio Pontelli (1488), designer of the castle at Ostia (1483–1486) . Jesi was the birthplace of the emperor Frederic II .

(1194), and also of the musical composer, Giovanni Battista

Pergolesi (1710-1736) . The river Aesis formed the boundary of Italy proper from about 250 B.C. to the time of Sulla (c . 82 B.C.); and, in Augustus' division of Italy, that between Umbria (the 6th region) and Picenum (the 5th) . The town itself was a colony, of little importance, except, apparently, as a recruiting ground for the Roman army .