Nereus and Achilleus were Roman soldiers of the Praetorian Guard (the emperor’s bodyguards) who were martyred at the end of the first century, and were said to have been baptized by St. Peter himself. When they became Christians they gave up their posts which they saw as immoral and were exiled and then killed under the reign of the emperor Trajan.
An epitaph written by Pope Damasus says the following: "Nereus and Achilleus the martyrs joined the army and carried out the cruel orders of the tyrant, obeying his will continually out of fear. Then came a miracle of faith. They suddenly gave up their savagery, they were converted, they fled the camp of their evil leader, throwing away their shields, armor, and bloody spears. Professing the faith of Christ, they are happy to witness to its triumph. From these words of Damasus understand what great deeds can be brought about by Christ's glory."
St. Pancras, or Pancratius, was a Syrian boy of pagan origin who went to Rome and was converted to Christianity. He was beheaded in 304 at the age of 14 during the persecution of the Emperor Diocletian. He is buried on the Via Aurelia in Rome and the church of St. Pancratius, which still stands today, was built on his grave in the fourth century.
Saints Nereus, Achilleus and Pancras have been honored together on May 12 since the fourth century.