Castra Nova equitum singularium The Castra Nova equitum singularium was an ancient Roman fort in Rome housing part of the emperor ' s cavalry bodyguard . The site of the fort now lies beneath the Basilica of St John Lateran . The " Castra Nova " , or " new fort " , was one of two cavalry forts that provided a base in Rome for the mounted bodyguard of the Roman emperors ( the " Equites singulares Augusti " ) . The Castra Nova ( " new fort " ) was so - called because it was the newer of the two forts , built to house an enlargement of the cavalry guard . Their previous fort " Castra Prioria " which lay not far away to the north had been built earlier , possibly under the emperor Domitian , and still housed the original force of 1500 mounted troopers . The full name of the fort is " Castra nova Equitum singularium Augusti " . History . The fort can be precisely dated to AD 193 , at the beginning of the reign of Septimius Severus . The new camp was necessitated by this emperors increase of the size of his cavalry guard from 1 , 500 to 2 , 000 men . The site of the camp was always speculated as being beneath the cathedral of St John Lateran ( Basilica di San Giovanni in Laterano ) , but it was identified definitively by excavations between 1934 and 1938 undertaken by Enrico Josi . Josi had obtained permission to explore the area of the basilica ’ s nave in advance of the construction of a new reinforced concrete floor . Within days it became clear that the remains of the Castra Nova existed in good condition just below the floor level and that the excavation was including a large part of the " principia " ( headquarters ) building . The completed excavations were then published by Colini . A large two - storey storage building and two barracks were also uncovered , but the greatest interest centered around the " principia " as its two strong rooms were very well preserved as were several office rooms . On the completion of the investigation the remains were preserved beneath the basilica ( along with the remains of the Constantinian cathedral and a Neronian " domus " ) in a spectacular underground archaeological park . The " curatores " inscriptions . On August 13 , 1934 , an ionic capital was uncovered within one of the headquarters rooms ( room “ ε ” on plan above ) , lying beside a short granite column that was still set into the floor . Upon the capital two inscriptions had been carved on behalf of an association of " curatores " , soldiers who were the grooms for the garrison horses . The first text was dedicated in 197 AD on 1 January in the consulship of Rufinus and Lateranus . The " Equites " were known to have served at the Battle of Lyon on the 19th of February , though evidently these men did not . The inscription records the dedication of the " schola curatorum " to Minerva Augusta , indicating that the " collegium curatorum " itself had only recently become in possession of an official meeting room that they could consecrate . The second inscription was dedicated in 203 AD " ob reditum ab expeditione felicissima in urvem sacram " i . e . on the return of the guards to Rome following their escorting of the imperial family . The " expeditione felicissima " may refer to the entire series of events since the " equites singulares Augusti " left Rome in AD 197 . The toppling of the capital furthermore provided historical evidence attesting to the destruction of the Castra Nova by Constantine ’ s forces and providing a " terminus ante quem " for both the dissolution of the " collegium " as well as for the camp itself .