The lower decumanum, popularly known as Spaccanapoli, represents one of the most prominent thoroughfares in the historic center of Naples, Italy.

Together with the major decumano (Via dei Tribunali) and the upper decumano, Spaccanapoli forms part of the three main streets of the urban layout of ancient Naples during Greek times. Originally, instead of "decumano", which is the designation of Roman times, it would be more appropriate to refer to it as "plateia", in conformity with the original Greek designation.

Spaccanapoli gained prominence from the Middle Ages until the 19th century for housing convents of religious orders and residences of influential figures. Its nickname, "Spaccanapoli" (literally, "Parthenapoli"), is due to its perfect rectilinear layout, which clearly divides the historic center between north and south.

Initially, the street stretched from Piazza San Domenico Maggiore to Via Duomo. During Roman times, it extended as far as the area of today's Piazza del Gesù Nuovo, as evidenced by the remains of the Roman baths found under the cloister of the Basilica of Santa Chiara.

During the Renaissance, the street underwent significant modifications, with the remodeling of Gothic buildings and the construction of new structures in place of demolished ancient palaces. Prominent Neapolitan Renaissance architects, such as Giovanni Francesco Mormando and Giovanni Francesco di Palma, contributed projects such as Palazzo Marigliano and Palazzo Pinelli.

In the 16th century, Viceroy Don Pedro de Toledo carried out an expansion towards the hill of San Martino and aligned the decumanum with an artery of the Quartieri Spagnoli to connect them to the city center and improve communications.

Between the 17th and 18th centuries, further modifications were made to civil and religious buildings. In the 19th century, some palaces were restored to their original form because of their historical importance, and in the 20th century, due to the Second World War, the church of Santa Chiara recovered its Gothic façade hidden by 18th century stuccoes.

The decumanum is divided into three sections: the first, from Piazza del Gesù Nuovo to Via Benedetto Croce; the central part, Via San Biagio dei Librai; and the final section, Via Giudecca Vecchia in the Forcella area, after the junction with Via Duomo.

The modern conception of "Spaccanapoli" includes extensions made in the 16th century, which prolonged the initial section up to the Quartieri Spagnoli. Thus, the decumano begins in Via Pasquale Scura at the top of the Quartieri Spagnoli, passes along Via Toledo in the central part and culminates in the Forcella part. In Via San Biagio dei Librai, it intersects with Via San Gregorio Armeno, one of the thistles that ascends northward, connecting the lower decumanum with the major one.