During the the Decian persecution of Christians under the emperor Decius (emperor from 249-251) the imperial Roman government issued tickets (libelli), indicating that citizens had satisfied the pagan commissioners by performing a pagan sacrifice (sacrificati), or burned incense (thurificati), demonstrating loyalty to the authorities of the Roman Empire. The government also issued libellatici (certificates) certifying that apostates had renounced Christianity.
Among the thousands of papyri excavated from Oxyrhynchus in Egypt, four papyri (POxy 658, POxy 1464, POxy 2990 and POxy 3929) are libelli issued during the year 250. (A total of 46 libelli from the year 250 have been published.)
"Participating in pagan sacrifices was a sin for Christians and punished by excommunication, because the New Testament forbade Christians to either participate in 'idol feasts' or to eat 'meat sacrificed to idols'. However, not participating made one liable to arrest by the Roman authorities. A warrant to arrest a Christian (POxy 3035) was also found at Oxyrhynchus, this too has been dated precisely—to the year 256. The grounds for this arrest are not documented, however, and it predates the persecution under the emperor Valerian by about a year.
"At various times under Roman rule, failure to sacrifice was punishable by death. Christian theologians (for example Cyprian) debated whether the threat of the death penalty mitigated the sin of having communion with idols, leaving room for forgiveness and restoration to the Christian community" (Wikipedia article on Libellus, accessed 02-02-2013).