The 3rd century Aurelian Walls stretched for 12 miles around the city. Measuring a distance of 12 miles in circumference, the defensive circuit is Rome's largest ancient building. There a dozen gateways in the wall, each of which provided access to a paved highway. Among them was the Via Ostiense, which linked Rome to the administrative city of Ostia. The gateway leading to Ostia (called Porta San Paolo today) houses a small and scarcely visited museum. The galleries display an interesting collection of maps, photographs, models, and archeological objects that were excavated in the area, while the walkways along the wall offer excellent views over the adjacent Piramide (Gais Cestius's pyramidal tomb).