Monuments and archaeological areas are often colonized by infesting plants, many of which produce allergenic pollen that can cause allergic symptoms in sensitive subjects. Pollen monitoring was carried out by a portable volumetric spore trap in some Roman archaeological areas and in two small cities in Latium (Central Italy), before and after a chemical treatment to eradicate infesting plants of Parietaria spp. to control the quality of the air. Results indicate that the herbicide treatment reduced the presence of Parietaria plants and their pollen concentration in the air in the sites which were the subject of this study.