The ancient city of Nicaea, located in the Iznik district of Bursa, preserved its feature of being an important center from the Hellenistic Period to the Ottoman Period. In the city, where most of the remains from the Roman period have either been damaged or lie buried beneath the traditional residential area, the most monumental structure attesting to this period is the theatre. The first reliable information regarding the construction stages of the theatre has been obtained through the correspondence between historian and writer Plinius the Younger, who was appointed as the governor of Bithynia, and Emperor Trajan. All details mentioned in the letters, including the changes and additions made during the construction stages, have been confirmed through recent excavations. The Nicaea theatre is the only example within Türkiye’s borders where seating rows (ima cavea) have been fully restored using vault and arch technology. The trapezoidal vaults supporting the lower cavea, the barrel vaults supporting the middle cavea, and the pillars supporting the upper cavea contribute to the structure of the building while also facilitating human circulation. Built with meticulous craftsmanship, the Nicaea theatre is a structure that reflects Roman characteristics while also embodying a uniquely Anatolian identity when compared to its contemporaries. As such, it possesses architectural heritage value that must be preserved. Especially; It stands out with its features such as having reliable historical information about the construction stages, hosting different cultural layers, designing in a hybrid plan, being elevated with a vaulted infrastructure, and having a basilica space, which is not common in Anatolian theatres. In 2024, The Recording, Restitution, and Restoration Project of the Roman Theatre at Nicaea have been applied to protect the multi-layered character, prevent physical destruction and transfer to the future generations in accordance with conservation principles.