The so-called ‘Great Baths’ were built in the 4th cent. A.D. and had an area of approximately 25,000 square meters. The archaeological excavations had so far brought to light three very large halls with refined geometric and figurative mosaic pavements or inlay-work floors, six pools for cold baths, the central part of the natatio and some sections of the heated halls on the western side. One epigraph found in the 1980s tells us their ancient name: “Thermae felices Constantinianae”.

At the end of the 5th cent. the Great Baths had lost their function and were inhabited by small family groups who buried their dead outside the perimeter of the building. Towards the end of the 7th century, their ruins were abandoned, probably because the vaults had begun to collapse. From the 13th century all the walls were dismantled to recover stone blocks and bricks and the whole area of the complex was reclaimed and given over to farming.

During the 20th cent. the Great Baths were investigated several times: by G.B. Brusin (1922-23), L. Bertacchi (1961) and P. Lopreato (1980-1987). In 2002 (until 2014) the University of Udine has resumed excavations on the basis of a joint research project with the Archaeological Superintendency of Friuli Venezia Giulia.

The 2016 archaeological campaign (under concession to the excavations) was focused in the northeastern area of the Great Baths, where we found a complicated stratigraphic sequence with three main phases.
1. The oldest evidence is a large foundation of bricks and lime mortar, covered with ‘cocciopesto’. It was probably a monumental complex with basins for water (one of which is circular) and with a channel for adduction and drainage of water. Its limits have not yet been fully brought to light and it could also be an earlier building, possibly connected to the nearby theatre and to one of the gates in the Republican walls.

2. This structure (maybe a monumental fountain) was partially dismantled and partly reused as foundation of the mosaic in large tesserae which covered the pavement of a room on the north side of the Great Baths.

3. In the 5th century this hall was divided into two smaller rooms with tessellated pavements. One of the mosaics had large trapezoids probably surrounding a central octagon; the only preserved scene shows a Nereid riding a Triton, nowadays exhibited in the Archaeological Museum of Aquileia.
Some thin and dark layers on the surface of the latest mosaics testify to a reoccupation in the Early Middle Ages.

An intensive and systematic despoliation has removed all the walls and most of the other structures, saving only few mosaic fragments and the deepest foundations and making difficult to reconstruct the different phases.