Italian officials were working Wednesday to defuse an unexploded World War II-era bomb found near the Formia train station, causing the closure of the main road and rail line between Naval Support Activity Gaeta and Naples.

The discovery of the 500-pound bomb led to the evacuation of up to 5,000 families from Formia, according to the city’s Web site. Ten American families also were moved to hotels in the Gaeta area at government expense, U.S. Navy officials said.

Italian news reports said that the evacuation could last until Monday.

Naval Support Activity Gaeta is located a few miles along the coast west of Formia, and road traffic between the small base and Naples travels through the town.

All of the 150 military and civilian employees at the small base live in Gaeta or surrounding towns, including Formia, as there is no on-base housing.

The 6th Fleet flagship USS Mount Whitney is based in Gaeta, but has been in the western Mediterranean taking part in a NATO exercise for about a week, so its crew is not affected.

The bomb was found by a farmer plowing a field near the station, according to the ANSA news agency.

Finding unexploded ordnance in the area is not uncommon. The Air Force Historical Studies Office’s Combat Chronology of World War II shows numerous bombings of Formia between September 1943 and the town’s capture in May 1944, with at least five separate air attacks in April 1944 alone.