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They were two thieves commonly known as Dismas (or Dysmas) and Gestas (or Gistas). It is said, but not proved, that they were cousins. They were condemned to be crucified also by Pilate for being robbers and vicious. Both had assasinated a woman that traveled from Jerusalem to Joppa, stolen the holy vessels of the Temple and Gestas had also stripped naked the daughter of Caiaphas, Sarah by name, who was priestess of the sanctuary. They remained in prison for a long time waiting for the acomplishment of their sentences. When Pilate put Jesus to death, he ordered that these two thieves were also crucified that same day. They suffered a dreadful punishment. They were flagellated
The Calvary

Mary of Magdala, the Veronica, the thief Dismas, Mary, Jesus, the centurion Longinus, the thief Gestas and women of Jerusalem

and carried with crosses to the hill of Calvary alongside Jesus. On arriving there, they were the first to be crucified. The executioners ordered them to pull their clothes away and gave them a loincloth. To appease the pain, they were allowed to drink some myrrh mixed with vinegar that a group of merciful women offered them. Then they were tied and nailed to their crosses. They screamed out in pain and probably fainted. Once crucified, at the beginning both mocked Jesus, but Dismas finally saw Jesus as our true Saviour and asked Jesus to be forgiven of his misdeeds.
Jan Coussiers ++

Christ and the two thieves crucified at Calvary. Based on a paiting by Jan Coussiers (XVII th century).

He understood that his cross was not just an instrument of torture, but of redemption. Gestas did not. According to a legend, after mocking Jesus, Gestas' eyes were mercilessly pecked out by a crow. They survied the death of Jesus, but when evening was approaching, and in order to hasten the agony, the executioners applied them the 'crurifragium' or breaking of legs. They died soon, but not without screaming and cursing. The executioners took the corpses and wrapped them in dirty rags. They were buried in a mass grave.