Inscription
IMP. CAES. LVCIO. SEPTIMIO. M. FIL. SEVERO. PIO. PERTINACI. AVG. PATRI. PATRIAE. PARTHICO. ARABICO.
PATHICO. ADIABENICO. PONTIFIC. MAXIMO. TRIBVNIC. POTEST. XI. IMP. XI. COS. III. PROCOS.
IMP. CAES. M. AVRELIO. L. FIL. ANTONINO. AVG. PIO. FELICI. TRIBVNIC. POTEST. VI. COS. PROCOS.
ET OPTIMIS. FORTISSIMISQUE. PRINCIPIBVS
OB. REM. PVBLICAM. RESTITVTAM. IMPERIVMQVE POPVLI. ROMANI. PROPAGATVM// INSIGNIBUS. VIRTVTIBVS. EORVM. DOMI. FORISQVE S.P.QR.
or
To the Imperator Caesar Lucius Septimius, son of Marcus, Severus Pius Pertinax Augustus, father of his country, conqueror of the Parthians in Arabia and Assyria, Pontifex Maximus, with Tribunician powers 11 times, triumphing general 11 times, consul 3 times, and proconsul; and to the Imperator Caesar Marcus Aurelius, son of Lucius, Antoninus Augustus Pius Felix , with tribunician powers 6 times, consul, proconsul, father of his country—**the best and bravest of princes**—on account of the republic restored and the empire of the Roman people increased by their outstanding virtues at home and abroad, the Senate and the Roman people dedicate this arch.
The Latin inscription on the Arch for Septimius Severus, which was originally decorated in gilded bronze lettering, honored the emperor and his two sons, Caracalla and Geta. It described how Severus and his sons “restored the Republic and expanded the dominion of the Roman people”[1] and included a lofty number of honorifics for each of the rulers. The inscription was later amended after Geta was murdered by Caracalla in 212 CE. As a result, Geta suffered damnatio memoriae, meaning that all images of and references to him were destroyed. Thus, in the present day, his name is no longer part of the inscription.
Brilliant, Richard. The arch of Septimius Severus in the Roman Forum. Rome: American Academy in Rome, 1967.