Crucifixion was a Roman method of execution normally reserved for slaves, rebels and provincials who held no Roman citizenship, carried out publicly and designed to prolong suffering and to warn onlookers rather than simply to kill. Two writers outside the Christian tradition mention Jesus's death by this method within about a century of the event. Tacitus, a Roman senator writing around 116 CE, records in his Annals that Christus was executed under the procurator Pontius Pilate during the reign of Tiberius, mentioned only because Tacitus is explaining the origin of the Christians he elsewhere describes as a troublesome sect.
Josephus, a Jewish historian writing in the 90s CE, includes a passage on Jesus in his Antiquities of the Jews known as the Testimonium Flavianum; most specialists judge that a later Christian scribe expanded an original, more restrained notice, but hold that a core reference to Jesus's condemnation under Pilate is authentic to Josephus.
Taken together with the Gospel accounts, modern historians of every stripe, believing and skeptical alike, count crucifixion under Pilate among the most secure facts available about Jesus, in contrast to material about him that is more contested. The Gospels themselves disagree on points of dating and sequence, including whether the crucifixion fell on Passover itself or the day before it, a discrepancy this entry records without resolving.