ROME, ITALY—Sediment cores taken near the mouth of the Tiber River have revealed the location of Ostia’s harbor. Located to the northwest of the ancient port city, the harbor was as deep as a seaport in order to receive ships carrying wheat for Rome’s citizens. This oldest part of the city, where an imperial palace has also been found, dates to the fourth century B.C. Flooding of the Tiber during the imperial period silted up the harbor and closed the port. Archaeologists now want to know how ships carried goods to Rome for the 25 years between the closing of the port and Ostia and the construction of Portus, a new harbor to the south of the city.