The answer is: 3 years

Acts 20:31

Paul's three-year stint in Ephesus was significant for several reasons. Ephesus wasn't just another stop on his journeys; it was a bustling urban hub, home to the Temple of Artemis, one of the Seven Wonders of the Ancient World. This city had a thriving trade and cultural scene, making it an ideal location for spreading his message. It was in this energetic environment that Paul held daily discussions at the School of Tyrannus, essentially nurturing a new generation of followers and laying the groundwork for what would eventually become a vibrant Christian community.

His time there also saw remarkable events, including miraculous healings and conflicts with local silversmiths upset by the decline in demand for Artemis shrines due to the growing popularity of Paul’s teachings. Interestingly, towards the end of his stay, Paul’s farewell to the Ephesians in Acts 20:31 serves as a heartfelt reminder of the bonds he formed.

Before leaving, he warned them about future challenges, echoing similar sentiments from Jesus' teachings about the trials they might face. This Ephesus connection had a long echo in Christian history, too, with the later dispatch of the "Epistle to the Ephesians," where themes of unity and community that Paul cultivated in those years are well embodied. Ephesus holds a remarkable place in the narrative of early Christianity, showcasing how one man's journey and dedication can alter the spiritual course of many.