The photo shows a Roman weight, which was used to weight fishing nets. The object is dated to the 1st century CE.
Due to the fact that the object was found on the remains of the Roman theater in Lisbon, scientists believe that the weight was used when constructing the structure. The weight was suspended on a rope and inserted into a hole in the building’s ground to assess whether the surface was even.
This type of ceramic weight was used by slaves once foremen used bronze weights (such were also found in Lisbon).