Present day Poreč, and Parentium in the past, has a regular, orthogonal street layout as did most ancient Roman towns. In case of Poreč, its layout has been preserved.

All planned Roman towns had a regular orthogonal street layout i.e. all the streets were crossing at a right angle building rectangular blocks. Poreč or Parentium in Antiquity, has preserved its ancient street layout with the former main Roman street of Decumanus Maximus as the lifeline of the town of Decumanus. As the main transversal street was called Cardo Maxiums, all other streets were named cardo and decumanus. Decumanus streets in Poreč are those which run along the longer side of the peninsula, from east to west, while those going in the north-south direction are called cardo.

Such a layout extended onto the town land surrounding it and forming its ager. Both layouts were supposed to be identical. However, as Poreč is located on the peninsula, it was only partially achievable.