One of the earliest uses of the word Christian surviving on papyrus is Papyrus Oxyrhynchus 3035 (P. Oxy. XLII 3035), a warrant for the arrest of a Christian issued on February 28, 256 by the authorities of the Roman Empire.
"The order was issued by the head of the Oxyrhynchus ruling council, to the police in a country village, to arrest a man described as a Christian (note χρισιανόν, the papyrus has the early spelling, χρησιανόν). The charge which makes the Christian liable for arrest is not given, unless this is Christianity itself. Persecution could explain this document, but Christians were generally tolerated by the authorities, periods of systematic persecution stand out as distinctive and exceptional in other documentation. One such period, however, was 'instituted under the emperor Valerian in AD 257 and 258.'
The manuscript is dated precisely in its closing lines to the third year of the co-regency of Valerian and Gallienus his son. We know this year to be 256 AD. The day and month are also provided in the last line. Phamenoth is the name of a month in the Egyptian calendar. It is called Paremhat in the Coptic calendar. The warrant was issued on the third day of this month. The equivalent date in our Gregorian calendar is 28 February 256 AD" (Wikipedia article on Papyrus Oxyrhynchus 3035, accessed 02-02-2013).