 This increase, in both trade and population, placed stresses on the limited space available in the Forum Boarium and underlined the importance of the river link to Rome's main port at Ostia.The Porticus and the Emporium appear to have worked together to facilitate the unloading, storage, and possibly redistribution of goods and foodstuffs, including imported grain for the corn dole, and appear to have been in continuous operation until the 6th century CE.The "opus incertum" building, in the form of a thin rectangle running parallel to the Tiber, was very large; approximately long, deep and subdivided by 294 pillars in rows of seven.