The casket was uncovered in the area of Lazio believed to the site of the ancient Roman city of Gabii, located 18 kilometres east of Rome.
Both caskets are made of lead and are believed to date from the 1st or 2nd century AD.
The second casket was found just a few metres from the first one, which was unearthed in 2009 by archaelogists working on the same dig, the 'Gabii Project', which began in 2007.
According the site director, archaeologist Anna Gallone, the two sarcophagi are examples of a unique local burial custom found in Gabii.
"The massive use of lead in the tombs is unique, it has never been seen before in central Italy," Gallone told Adnkronos International (AKI).
Gabii was a rival of ancient Rome and the original site extended over 60 or 70 hectares.
The complex history of this important city is currently being investigated by team led by Nic Terrenato of the University of Michigan, made up of over 70 American students and 20 graduates and archaeologists.
"It is probably the largest US-led excavation in Italy," Gallone told AKI.