Deceased Italians are usually placed in “niches” in the cemetery, which are leased,  most for 99 years allowing for at least 3 “burials”.  In the newer sections of the cemetery the lease
is for only 33 years earning more money for the church (or city).  Once the body has decomposed, this usually takes from 10-30 years, the bones and
ashes are transferred to the “ossario”, a smaller vault within the cemetery, leaving space for the next family
member.  Most of the niches contain a
ceramic photo of the deceased along with a vase for flowers and an eternal
lamp.  If the lease runs out and is not
renewed the bones are eventually transferred by the city (or church) to the
underground, communal bone vault through a trap door in the floor.  In November each of the niches are decorated
with mini lights for the All Souls Day celebration on November 2^nd.

All of the above means that unless your ancestor was famous, or rich you are unlikely to find a gravestone in the cemetery or the exact location of their ashes.