IESI (anc. Aesis), a town and episcopal see of the Marches, Italy, province of Ancona, 17 m. W. by S. from Ancona town by rail, 318 ft. above sea-level. The pop. of the commune in 1931 was 29,090. It lies on the left bank of the river Aesis (mod. Esino). It still retains its picturesque mediaeval town walls. S. Marco is an interesting 13th century church. The Palazzo del Co mune is a fine, simple, early Renaissance building (1487-1503) by Francesco di Giorgio Martini. The courtyard with its loggie was built by Andrea Sansovino in 1519. The picture gallery con tains some good pictures by Lorenzo Lotto. The castle was built by Baccio Pontelli (1488) . Iesi was the birthplace of the emperor Frederic II. (1194), and also of the composer Giovanni Battista Pergolesi (1710-1736). The silk spinning industry is of consider able importance. The Aesis formed the boundary of Italy proper from about 25o 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).
See L. Marinelli in Cronache d'Arte iv. (1928) "Le Mure di Iesi."