Ucetia was previously known only by name for thousands of years, with many questioning its existence entirely.
The city was believed to have existed since before the Roman conquest of Great Britain in 43 AD.
Now a top team or archaeologists have uncovered the elusive metropolis near Uzes, in southern France.
Led by Philippe Cayn from the French National Institute for Preventive Archaeological Research (INRAP), the team uncovered a 4,000sqm city decorated with elaborate mosaics.
Staggering footage shows off one intricately designed piece which shows a sun surrounded by an owl, deer, duck and eagle as well as ocean waves.
While another piece is made up of a variety of circles, diamonds and triangles – perfectly framed within a triangle.
Mr Cayn said: ”Prior to our work, we knew that there had been a Roman city called Ucetia only because its name was mentioned alongside 11 other names of Roman towns in the area.
“It was probably a secondary town, under the authority of Nimes. No artefacts had been recovered except for a few isolated fragments of mosaic.”
French government officials called for the excavation in October after buying up land near Uzes to build a boarding school.
And just months later, the experts had uncovered the whole lost city and salvaged dozens of beautifully crafted mosaics.
They also found the site had been occupied since 1st century BC, as they discovered remains of huge walls dating back to the Roman conquest.
A kitchen-style room where a bread oven was set up was also discovered, but the researchers are still unclear as to what kind of building the mosaics were being housed in.
The excavations will continue at the site until August 2017.