Short answers, pulled from the story.
The marble plaques emerged from the earth during construction work by the Santacroce family between 1598 and 1641. Records noted them in 1629 and again in 1631 while they remained visible there until documentation confirmed their presence in the courtyard in 1683.
One portion resides at the Louvre museum with inventory number Ma 975. Another piece sits within the Glyptothek collection in Munich bearing inventory number 239. A copy of that second panel can be viewed inside the Pushkin Museum in Moscow.
The scene marks the beginning of the Roman census when all citizens were recorded to determine senate membership and military service. The scene might depict the censorate of Cn. Domitius Ahenobarbus and L. Caecilius Metellus in 115 BC.
A general probably named Cn. Domitius Ahenobarbus vowed to build a temple after a naval victory likely occurring off Samos in 129 or 128 BC against Aristonicus. The construction of the temple dates to 122 BC when Cn. Domitius Ahenobarbus attained consulship.
The frieze is dated to the end of the second century BC based on armor details and represents the second oldest Roman bas-relief currently known. The first appears on a column erected by Lucius Aemilius Paullus Macedonicus honoring his victory at Pydna in 168 BC.