Lucius Caecilius Metellus Diadematus was one of the moneyers for the year 128 BC. He was the second son of Roman politician and general Quintus Caecilius Metellus Macedonicus, and served as Consuil in 117 BC.
During his consulship in 117 BC he supported the development of roads in Italy and he probably built Via Caecilia. A year later he was Proconsul of Cisalpine Gaul. In 115 BC Diadematus was elected Censor and during his censorship with Gnaeus Domitius Ahenobarbus they expelled 32 Senators from the Senate. He was an opponent of Lucius Appuleius Saturninus and when Saturninus in 100 BC tried to oppose the Senate by means of force, together with other Senators they went to arrest him.
During his consulship in 117 BC he supported the development of roads in Italy and he probably built Via Caecilia. A year later he was Proconsul of Cisalpine Gaul. In 115 BC Diadematus was elected Censor and during his censorship with Gnaeus Domitius Ahenobarbus they expelled 32 Senators from the Senate. He was an opponent of Lucius Appuleius Saturninus and when Saturninus in 100 BC tried to oppose the Senate by means of force, together with other Senators they went to arrest him.