In Roman city planning, a cardo or cardus was a north-south-oriented street in ancient Roman cities, military camps, and colonia The main street of the city was most often the cardo and was sometimes called the cardus maximus. The cardo served as the center of economic life. The street was lined with shops, merchants, and vendors.

Most Roman cities also had a Decumanus Maximus, an east-west street that served as a secondary main street. Due to varying geography, in some cities the decumanus is the main street and the cardo is secondary, but in general the cardus maximus served as the primary road. The Forum was normally located at the intersection of the Decumanus and the Cardo.

The cardo was the "hinge" or axis of the city, derived from the same root as cardinal. The term 'cardus' is derived from the north-south line the augurs would draw when making the auspices.

Cardo of Jerusalem

The Cardo in the Old City of Jerusalem is one good example. After the Jewish rebellion of 70 AD was crushed by Titus' troops, Jerusalem was refounded as Colonia Aelia Capitolina and its new city plan featured a long collonated cardo running from north to south, date from the time of Emperor Justinian in the 6th century AD. The cardo is still a street in modern Jerusalem.

Perhaps the most famous ancient map of Jerusalem, a 6th century mosaic map found in a church flor in Medeba, Jordan, portrays the cardo as the central axis of the city.

Cardo of Petra

The excavations at Petra in Jordan have unearthed the remains of an ancient Roman city on the site, with the main feature of the city being a collonated cardo. The original road survives.