The most ancient Jewish ritual bath outside of Israel has been unearthed at the Archaeological Park of Ancient Ostia. It dates to the end of the 4th century. The mikveh, a bath used for ritual purification, was built in a narrow room with steps leading down into a pool deep enough to completely immerse an adult man of average height. A small earthenware oil lamp with a menorah and lulav (palm branch) engraved on it was found on the bottom, confirming its identification as a Jewish ritual bath rather than any other of the many different kinds of bathing environments found in Rome.

Located on the Tyrrhenian Sea near the mouth of the Tiber about 20 miles southwest of Rome, Ostia was the main port city of Republican and early Imperial Rome. The small harbor proved inadequate to the growing needs of the expanding empire and the harbor of Portus began to supplant it in the 2nd century. Ostia continued to grow in population through the 3rd century even as its commercial activities began a slow decline.

The research was able to concentrate in particular on the sector, called “Area A”, located in an absolutely central area of ​​the city , both from a topographical/urban and architectural point of view, as it is located near the ancient course of the Tiber and between the building of the Grandi Horrea to the west, the republican sanctuary of the Quattro Tempietti, the Mithraeum of the Seven Spheres and the Domus of Apuleius to the south, and the Piazzale delle Corporazioni to the east. Surprisingly , despite its centrality, this area had never been investigated previously and therefore appeared ideal for the new excavation activities, qualifying as an intact stratigraphic basin.

Given the site’s central location, archaeologists expected to find something connected to trade, perhaps a warehouse or a river port, but instead they uncovered the remains of a large, luxurious domus with black-and-white mosaic floors and frescoed walls that was at least two stories high. The excavation uncovered a kitchen, latrines, a portico and two ovens as well as the small immersion pool.

The semi-hypogeum is a small rectangular room, closed on the east side by a semicircular apse, which shows several construction phases. In the last one, it is accessible from the west side through a large marble threshold with a raised external edge and is occupied almost along its entire width by a staircase, consisting of three steps with notable traces of wear and flanked by two masonry jambs covered on the inside with hydraulic plaster; the floor level at the end of the staircase, made of bipedal bricks (60 cm square bricks), was placed at a level about 1 m lower than that of the entrance threshold and had a recess about 3 cm wide that continued on the side walls, most likely used to house a barrier, perhaps wooden. In the north-eastern corner, immediately above the northern jamb, there is a through hole in the masonry, probably intended to house a pipe for the supply of water.

At the eastern end of the floor there is a circular well with a diameter of 1.08 m, made of cement and crowned by a brick ring probably added at a later time, certainly intended for the collection of groundwater; at the connection with the floor, the perimeter of the well widens to form a sort of invitation. At a depth of 1.10 m from the mouth, the well narrows to a diameter of 1.00 m, forming a recess most likely functional for the positioning of a grate or removable wooden flooring.

The room was closed on all sides by walls built in opus listata (with blocks of tuff alternating with courses of bricks) without openings; on the apse at the back, in an elevated position, a niche was found, 0.60 m high and 0.45 m wide, covered in blue plaster and shells, framed by a pair of small columns covered in stucco resting on a surface supported by brick brackets.

The architectural features of the space — the steps across the full width, the use of hydraulic plaster, the well for collecting groundwater, the pipe conduit — are all characteristic of mikveh design. Rabbinic sources from the 3rd century prescribe that a mikveh must be supplied with at least 500 liters of fresh water (rain or spring) and that it be deep enough to immerse an adult man.

There was an organized Jewish community in Rome from the 2nd century B.C., and based on epigraphic evidence, one in Ostia in the middle of the 1st century. The oldest written evidence attesting to the presence of Jews in Ostia is a marble funerary marker found in a necropolis just southeast of Ostia Antica recording the burial of members of the Fabii Longii family “IVDAEI.” A synagogue was discovered in Ostia during highway construction in 1961. It was built in the 2nd century, rebuilt after an earthquake in 443 A.D. and remained in use into the 6th century when the port silted over and the city was abandoned. It is the oldest synagogue found outside of Israel.