What monumental structure did Emperor Justinian build that was the largest church in the world for centuries?

The monumental structure that Emperor Justinian built, which held the title of the largest church in the world for many centuries, is Hagia Sophia. Commissioned in 532 AD and completed in 537 AD, Hagia Sophia was designed by the architects Anthemius of Tralles and Isidore of Miletus. Its architectural innovation, particularly the massive dome that appears to float above the central nave, was a significant achievement in Byzantine architecture and has influenced many later religious buildings, particularly in its design approach.

Hagia Sophia initially served as a cathedral and remained the centerpiece of Orthodox Christianity for nearly a thousand years until the fall of Constantinople in 1453 when it was converted into a mosque. Its scale, intricate mosaics, and harmonious proportions exemplify the peak of Byzantine architecture. Because of its significant historical and architectural importance, it remained the largest cathedral in the world until the construction of St. Peter's Basilica in the 16th century.

The other structures mentioned also hold historical significance, but they do not match the context of this question regarding Emperor Justinian or the record for the largest church.