Line C:

The project for Line C of the Rome Metro, the third line envisaged by the Town General Plan, aims to directly connect currently distant areas and neighbourhoods by crossing the city from northwest to southeast. Once completed, Line C will increase the development of the existing metro network by more than 50%.

The "Fundamental Route" of Line C, extended over a length of 25.5 km and equipped with 29 stations, begins on the surface in the territory of the Municipality of Monte Compatri and follows the route of the existing Termini-Pantano railway. Subsequently, it descends underground just before the Grande Raccordo Anulare, crossing the historic centre to the Mazzini neighbourhood. Along its route, Line C intersects Line A (San Giovanni and Ottaviano), Line B (Colosseo), the future Line D (Venezia) creating an effective "network effect".

The route, now fully funded, is divided into sections whose construction began with those further east: T2 under design, T3 under construction, T4-T5, T6 and T7 with the Granite Depot/Workshop, completed and operational. The subdivision of the Fundamental Route into sections derives from the different progress state of the designs at the time of the inclusion of the work in the Objective Law (2003), with the consequent approval and financing procedures. 

The route of the T3 Section, which falls entirely within a historical-monumental context unique in the world, develops for a total length of about 3 km from Piazzale Appio to Via dei Fori Imperiali. The project includes 2 stations, Porta Metronia and Colosseo/Fori Imperiali, two multifunctional shafts, respectively in the gardens of Via Sannio and Piazza Celimontana, and 2 line tunnels of 5.8 m in diameter each, almost entirely made with TBM.

The part of Section T3, which includes the line tunnels from San Giovanni to Via Sannio (built using the traditional method), the multifunctional shaft in Via Sannio, and the section of the line tunnels to Porta Metronia Station (built using mechanised excavation through TBM), has already been delivered to the Administration with minutes of advance delivery art. 200 Presidential Decree 554/99 dated 18/06/2021, and was then subject to the authorisation for operation by Lazio Region Decree No. G10991 dated 11/08/2022. The early completion of this part made it available to the Merchant a railway communication (at the multifunctional shaft) through which the reversal of the trains upstream of the current provisional terminus of San Giovanni can take place, thus allowing the use of both station platforms.

At the moment, the construction of the remaining part of the Section is being completed, with the two stations and the Celimontana shaft: the civil works are substantially completed and progress is being made with the architectural finishes and the plant part, both station and line. As of 31/12/2023 (SAL 63 as of 31/08/2023) there is a total accounted amount of € 583,118,525.58 plus VAT, which represents about 86% of the total contractual amount (€ 676,601,467.92 plus VAT). The net amount accounted for the works only is € 492,322,455.73 plus VAT, corresponding to about 89% of the total reference amount from the updated Economic Framework, which amounts to € 553,539,226.11 plus VAT.

In particular, the value of the works of the stations with respect to the total works (about 550 million euros) amounts to: about 90 million for the Porta Metronia station, 120 for the Colosseo/Fori Imperiali station, 200 for the line tunnels, 80 for the plants, and 60 for the remaining items (shafts, special works and more).

Porta Metronia Station:

The station is located in a strategic position between the stations of San Giovanni (interchange between Line C and Line A) and Colosseo/Fori Imperiali (interchange between Line C and Line B), about 500 metres south of Piazza San Giovanni in Laterano, and 300 metres from the entrances of the hospital of the same name. It is bordered to the north by Via dei Laterani, to the west by Piazzale Ipponio, to the south by Via Farsalo, and to the east by the "La Romulea" sports fields.

The building, made with the top-down method between reinforced concrete diaphragms, extends for about 120 metres in length, 28 metres in width, and over 30 metres in depth, divided into five levels. The station follows the typical layout of Line C, with a central platform about 110 metres long and about 4 metres wide.

During archaeological excavations, a military complex dating back to the 2nd century AD was found, including a "barracks" and a "domus del Comandante", which is believed to have been abandoned and partially buried in the second half of the 3rd century AD. This discovery, considered one of the most important of recent years for its unity and conservation, required a redefinition of the project to allow the conservation and relocation of archaeological structures.

The Special Superintendence of Archaeology, Fine Arts, and Landscape of Rome therefore ordered the temporary relocation of the archaeological structures—it took care of their restoration—and a redefinition of the project. This was done to allow their relocation in situ, in the same position, restoring the visual relationship with the Aurelian Walls. A design variant was therefore necessary, providing for the transfer of a part of the station body and the creation of a large museum area with ticket office, wardrobe, and refreshment area that will make the entire Roman structure visible, also through a walkway suspended above part of the structures found. By Approval Act No. 6/2021 dated 29 March 2021, the Roma Metropolitane Contracting Authority approved the variant executive plan, the implementation of which is in progress.

The entrances to the station will converge in a hypogeal square, which will provide access to both the museum area and the metro station, keeping the two functions separate but allowing passengers to appreciate the cultural value of the infrastructure.