Nicaea was an important city in the Byzantine Empire, located in present-day Turkey. It served as a significant center for trade and culture, especially during the early medieval period. Nicaea is best known for hosting the First Council of Nicaea in 325 AD, which was convened by Emperor Constantine to address issues within the Christian community, including the nature of Christ and the date of Easter. The city continued to play a vital role in Byzantine history, particularly during the Byzantine-Seljuk Wars. In 1204, Nicaea became the capital of the Byzantine Empire in exile after the Fourth Crusade led to the capture of Constantinople. It remained a key location until the eventual recapture of Constantinople in 1261.