Archaeologists have been probing the depths of the Eternal City at 38 digs, many of which are near famous monuments or on key thoroughfares.
Over the last nine months, remains - including Roman taverns and 16th-century palace foundations - have turned up at the central Piazza Venezia and near the ancient Forum where works are paving the way for one of the 30 stations of Rome's third subway line.
"The medieval and Renaissance finds that were brought to light in Piazza Venezia are extremely important for their rarity," said archaeologist Mirella Serlorenzi, who is working on the site.
Serlorenzi said that among the most significant discoveries in a ninth-century kitchen were three pots that were used to heat sauce. Only two others had been found previously in Italy.
The copper factory "factory" was used to work on copper alloys, and it consisted of small ovens, traces of which can be seen. Small copper ingots were found and are being analyzed.
The archaeological investigations are needed only for stairwells and air ducts, as the 15 miles of stations and tunnels will be dug at a depth of 80 to 100 feet - below the level of any past human habitation, experts said.
However, most of the digs still have to reach the earth strata that date back to Roman times, where plenty of surprises may be waiting. That may create problems between planners and conservationists, officials said.
"It is impossible that there will not be situations of conflict. We know that in some cases the conflict will create a removal of ancient ruins," Rome's archaeological superintendent Angelo Bottini told The Associated Press.
Under Italy's strict conservation laws, it will be up to Bottini's office for Rome to decide whether a find will be removed, destroyed or encased within the subway's structures.
Countless public and private works have been scrapped over the years in Rome and across Italy, and it is not uncommon for developers to fail to report a find and plow through ancient treasures.
Rome's 2.8 million inhabitants can rely on just two subway lines, which only skirt the center and leave it clogged with traffic and tourists.
Plans for a third line that would serve the history-rich heart of Rome have been put off for decades amid funding shortages and fears that a wealth of discoveries would halt work.
The $4.6-billion project is due for completion in 2015, but parts of the line are scheduled to open in 2011, with high-tech automatic trains to transport 24,000 passengers per hour.