Douglas Harper's Etymology Dictionary
rock face on the Capitoline Hill in Rome, from which persons convicted of treason were thrown headlong, from Latin (mons) Tarpeius "(rock) of Tarpeia," said to have been a Vestal virgin who betrayed the capitol to the Sabines and was buried at the foot of the rock. Her name probably is of Etruscan-Tyrrhenian origin.
Wikipedia
The Tarpeian Rock (; Latin: or , Italian Rupe Tarpea) was a steep cliff of the southern summit of the Capitoline Hill, overlooking the Roman Forum in Ancient Rome. It was used during the Roman Republic as an execution site. Murderers, traitors, perjurors, and larcenous slaves, if convicted by the quaestores parricidii, were flung from the cliff to their deaths. The cliff was about 25 meters high. There seems to be a belief that similar punishments were inflicted on the disabled and mentally ill but there are no reliable sources for that.
Usage examples of "tarpeian rock".
The corrupt or malicious witness was thrown headlong from the Tarpeian rock, to expiate his falsehood, which was rendered still more fatal by the severity of the penal laws, and the deficiency of written evidence.
In Rome, traitors were hurled from the Tarpeian rock, or slain in other, slower ways.
This Tarpeian rock was then a savage and solitary thicket: in the time of the poet, it was crowned with the golden roofs of a temple.
The Capitoline Hill, with the statues, and up there is the Tarpeian Rock where they threw traitors off—.
The deed executed by those of the Tarpeian Rock, Saturn in Leo February 13.
On the day he brought his army across the Marne, he was marked for the Tarpeian Rock.