Livia dupondius with Nero Countermark

IVSTITIA
Diad. and draped bust of Livia as Justitia right

TI CAESAR DIVI AVG F AVG P M TR POT XXIIII around large SC

Rome 22-23AD

Sear 1739

Countermark on reverse NCAP:
There are several interpretations of what this, the most interesting of all Julio-Caludian ctmk., means. The two most likely are:
1. Nero Ceasar Augustus Populi Romani
2. Nero Caesar Augustus Probavit
In the first instance it is a congiarium or public dole given by Nero to the people of Rome. In the second, it is a revalidation of the earlier coins of ones predecessors still in circulation.
Possible is also a later use, eg. by Nerva, or that no emperors name was part of the countermark, Countermark Martini Pangerl Collection 1; 20; 60 depending on subtype