A modern name for the scalae Gemoniae or "Gemonian steps". In classical Rome, a stair leading apparently from the West side of the forum down towards the Tiber. The corpses of executed criminals were exposed here to vultures, animals, and the abuse of the Roman people, afterwards being dragged down to the river with hooks and pitched on in. In the early empire (from about 16CE), members of the senatorial class, who had traditionally had the right to go into exile when convicted of a capital crime, began to be treated in the same way when accused of treason (maiestas).
The Roman emperor Vitellius suffered this fate, as did Sejanus, C. Nymphidius Sabinus, and most of the victims of Tiberius' purges. According to Suetonius (vit. Tib. 61) and Tacitus (annales, 5-6), some number of children came to the same end when Tiberius decided it would be most prudent or efficient to eliminate entire families at once.
The steps seem to have seen most use -- or, at least, the most high-ranking victims -- during Tiberius' terror (c. 30-37 CE). After that, except for a few more executions in 68-69CE (the year of four emperors), the practice appears to have waned. Cassius Dio, writing at the beginning of the third century CE, knows of the practice but refers to it (RH, 60.35) as something that used to be done in the days of the Julio-Claudians.
Sources:
Suetonius, De vita Caesarum.
Tacitus, Annales.
Cassius Dio, Roman History.