Peter and Paul are martyred in Rome
John 21:18–19; 2 Timothy 4:6–8; 2 Peter 1:14
Under Nero, both apostles were put to death in Rome: Paul, a Roman citizen, by the sword, and Peter by crucifixion, as Jesus had foretold.
For I am already being offered, and the time of my departure has come.
2 Timothy 4:6 (World English Bible)
Clement of Rome, writing about AD 96, spoke of Peter and Paul as the greatest and most righteous pillars of the church, who suffered and bore witness to the end. Later writers add that Paul was beheaded on the road to Ostia and that Peter asked to be crucified upside down, feeling unworthy to die as his Lord had.
Dating notes
Ussher, following Eusebius and Jerome, dates both deaths to AD 67 (Paul's to 29 June). Many historians prefer AD 64, during the persecution after the fire, up to Nero's death in AD 68.