Cardus Maximus is a term in ancient Roman city planning. It denotes a N-S oriented road in a Roman military camp or colonia. The main cardus is the Cardus Maximus. In the middle the Cardus Maximus crosses the perpendicular Decumanus Maximus, the other main road. The Forum is normally located at this intersection of the Decumanus Maximus and the Cardus Maximus.

The term 'cardus' is derived from the N-S line the augurs would draw when making the auspices.