Question: "What happened on Paul's fourth missionary journey?"
Answer: Paul took at least three missionary journeys covering Cyprus, Syria, Asia Minor, Macedonia, and Greece before he was wrongly accused in Jerusalem and imprisoned, first in Caesarea and then in Rome. What happened after this point is unclear. Some say that Paul’s trip from Caesarea to Rome for his first Roman imprisonment constitutes his “fourth journey,” while others say he embarked on another missionary trip after he was released. Much depends on whether he was imprisoned once or twice. In 2 Timothy 4:16, Paul, writing from prison, refers to his “first” trial, and verse 17 indicates that it ended favorably; these clues point to at least two imprisonments in Rome. It’s been conjectured that Paul’s fourth missionary journey started upon his release from his first imprisonment.
The book of Acts clearly outlines the first three of Paul’s missionary journeys and his first set of trials and ends with his first imprisonment in Rome. Everything after that time must be gleaned from Paul’s epistles, particularly the stops he mentions in the letters he wrote during his second imprisonment.
Possible places Paul visited include the following:
Crete (Titus 1:5)
Corinth (2 Timothy 4:20)
Miletus (2 Timothy 4:20)
Macedonia—possibly Philippi (1 Timothy 1:3)
Colossae (Philemon 1:22)
Troas (2 Timothy 4:13)
Ephesus (1 Timothy 3:14; 4:13)
Nicopolis (Titus 3:12)
There is a tradition that Paul went to Spain, but there is no record of this in the Bible. He did mention to the Romans that he wanted to take the gospel to Spain (Romans 15:24, 28). Clement of Rome’s AD 95 writings say Paul went to “the farthest limits of the West,” which could mean Spain or possibly the United Kingdom, and the Muratorian Canon (AD 180) says Paul went from Rome to Spain.
It is believed that Paul’s second arrest brought his fourth missionary journey to an end. He was sent to Mamertine Prison, which was much rougher than being kept in house arrest in his own lodgings. During his second Roman imprisonment, Paul knew the time of his departure from this world was near (2 Timothy 4:6). He was cared for by Luke (2 Timothy 4:11) and Onesiphorus (2 Timothy 1:16–17) but abandoned by many others. Nero was on a rampage against Christians in Rome and, if the tradition is true, Paul was beheaded at Nero’s order.