Hagia Sophia was the biggest church on Earth and went up in under six years, and that haste is part of why its first dome fell in 558.

• ✓Procopius, Buildings I.1 (Loeb, LacusCurtius)
• ✓Theophanes, Chronographia; Malalas, Chronicle 18; Agathias, Histories V.9 (Columbia translations)
• ✓EBSCO Research Starters: Hagia Sophia Is Built
• ✓R. J. Mainstone (1988), Hagia Sophia
• ✓Çakmak, Taylor & Durukal (2009), Soil Dyn. Earthquake Eng., doi:10.1016/j.soildyn.2008.07.007
• ✓Moropoulou, Çakmak et al. (2002), Constr. Build. Mater., doi:10.1016/S0950-0618(02)00005-3
• ✓Wikipedia: Hagia Sophia

Hagia Sophia was the biggest church on Earth, and it went up in under six years. That speed is part of why its dome fell. The mortar between the bricks was as thick as the bricks themselves, and it hadn't hardened. Under all that weight, the great piers began leaning outward. And on top sat a dome so shallow it seemed to float. Every arch pushes outward on whatever holds it up, and the flatter it is, the harder it pushes. A flat dome on spreading piers. Then the earthquakes came. In May 558, part of the dome crashed onto the altar. So they rebuilt it about twenty feet taller, because a steeper dome sends more of its weight straight down. The biggest church on Earth had to build its dome twice.