accessio

In Roman law, accessio is a principle that dictates ownership when one thing is joined to another. If an accessory item belonging to one person (A) is attached to a principal item belonging to another person (B), the ownership of the combined whole transfers to the owner of the principal item (B). A key application of this principle is that anything built upon land becomes part of that land and cannot be owned separately. For example, if person A's purple dye is used to color person B's cloth, the dyed cloth belongs entirely to person B. This concept highlights how Roman law determined ownership in cases of combined property.1