Latium adiectum or Latium Novum was a region of Roman Italy between Monte Circeo and the river Garigliano, south of and immediately adjacent to Old Latium, hence its name of attached Latium.

Old Latium is a region of the Apennine Peninsula bounded to the north by the Tiber River, to the east by the central Apennine Mountains, to the west by the Mediterranean Sea and to the south by Monte Circeo. It was the territory of the Latins, an Italic tribe which included the early inhabitants of the city of Rome. Later it was also settled by various Italic tribes such as the Rutulians, Volscians, Aequi, and Hernici. The region was referred to as "old" to distinguish it from the expanded region, Latium, that included the region to the south of Old Latium, between Monte Circeo and the river Garigliano – the so-called Latium adiectum. It corresponded to the central part of the modern administrative region of Lazio, Italy, and it covered an area measuring of roughly 50 Roman miles. It was calculated by Mommsen that the region's area was about 1860 square kilometres.