In Romancity planning, a decumanus was an east–west-oriented road in a Roman city or castrum. The main decumanus was the Decumanus Maximus, or most often simply the Decumanus. In a military camp this connected the Porta Praetoria to the Porta Decumana. This name comes from the fact that the via decumana or decimana separated the Tenth Cohort from the Ninth in the legionary encampment, in the same way as the via quintana separated the Fifth Cohort from the Sixth. In the middle, or groma, the Decumanus Maximus crosses the perpendicular Cardo Maximus, the primary north–south road that was the usual main street. The Forum is normally located close to this intersection of the Decumanus Maximus and the Cardo Maximus.
Examples
In the ancient Roman city ofBarcino, the Decumanus Maximus started at the late-Roman gate in front of the current Plaça Nova square. Within the city of Split in present-day Croatia is the UNESCO Roman monument, Diocletian's Palace. This city, built by the Emperor Diocletian, exhibits the characteristic Roman orthogonal street system with the Decumanus Maximus connecting the west Iron Gate to the east Silver Gate. In Roman Gadara, present-day Umm Qais in Jordan, the Decumanus runs east–west for approximately one kilometre with its ancient flagstones extant. Another fine example is the "Straight Street", Via Recta, in Damascus, which is 1,500 metres long, connecting the eastern and western gates. In Beirut's Central Business District, Rue Weygand, which runs east–west, still follows the ancient Roman Decumanus. In Florence, the Decumanus is preserved as the streets Via Strozzi, Via Speziali, and Via del Corso in the city's old centre. Although these streets have different names they form a continuous line with a split between the Via Strozzi and Via Speziali by the Palazzo Strozzi. Roman times, these three streets formed the Decumanus of Florentina, the name of the Roman colonia. The Via Roma and the Via Calimala are formed from the ancient Cardo, and what was once the Forum in ancient Florence is now the Piazza della Repubblica. In Naples, there still exist three main decumani which are, from west to east:
Superiore: consisting of Via Sapienza, Via Pisanelli, and Via Anticaglia