After the breaking of Porta Pia and the popular vote of 2 October 1870, Lazio was annexed to the Kingdom of Italy and Rome became its capital. King Vittorio Emanuele himself took up residence in the Quirinal.

Between 1871 and 1876, several proposals for fortifications for the defence of the unified state were evaluated.

In 1877, under the threat of a new French attack, the Royal Decree approved the defence of the capital by means of an entrenched camp, defended by 15 forts and three batteries.

- Fort Monte Antenne
- Fort Pietralata
- Fort Tiburtina
- Fort Prenestino
- Fort Casilina
- Fort Appia Antica
- Fort Ardeatina
- Fort Ostiense
- Fort Portuense
- Fort Bravetta
- Fort Aurelia Antica
- Fort Boccea
- Fort Braschi
- Fort Trionfale
- Fort Monte Mario

- Appia Pignatelli Battery
- Porta Furba Battery
- Nomentana Battery