Which architecturally significant structure is associated with Emperor Justinian?

The Hagia Sophia is the architecturally significant structure associated with Emperor Justinian. Built in the 6th century, it serves as an exemplary model of Byzantine architecture and represents a significant achievement in engineering and design. The Hagia Sophia was originally constructed as a Christian cathedral and later converted into a mosque, reflecting the historical and cultural shifts of the region.

One of its key features is the massive dome, which was an innovative advancement at the time and has influenced numerous structures throughout history. The use of pendentives allowed for the placement of a circular dome over a square room, creating a harmonious and grand space that is both visually and structurally impressive. Additionally, the interior is adorned with intricate mosaics and marble, showcasing the wealth and artistic capabilities of the Byzantine Empire.

The other options represent different cultural and historical contexts. The Colosseum is an ancient Roman amphitheater, the Parthenon is a temple dedicated to the goddess Athena from ancient Greece, and St. Peter's Basilica is a Renaissance-era church in Vatican City. While all are remarkable structures, they do not have a direct association with Emperor Justinian or the period of Byzantine architecture.