Santa Maria ad Martyres, also known as the Pantheon, is a former Roman temple that has been converted into a church. Located in Rome, it was completed around 126 AD during the reign of Emperor Hadrian. The building is renowned for its impressive dome, which remains the largest unreinforced concrete dome in the world. The structure is dedicated to the Virgin Mary and all martyrs, reflecting its Christian significance. Its remarkable architecture, including the oculus at the dome's apex, allows natural light to illuminate the interior. Santa Maria ad Martyres is a popular tourist destination and a significant example of ancient Roman engineering.