In addition to the baptistery, the archaeologists made several other discoveries at the Hagia Sophia (which means "holy wisdom") cathedral, located in what is today Istanbul.

Between 2004 and 2018, the researchers discovered previously unknown buildings, reconstructed what the cathedral's Patriarchal Palace looked like and even identified a spot where the Byzantine emperor once stood during a ceremony, said project leaders Ken Dark and Jan Kostenec in a recently published book, "Hagia Sophia in Context: An Archaeological Reexamination of the Cathedral of Byzantine Constantinople" (Oxbow Books, 2019).

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"Our fieldwork between 2004 and 2018 on the area surrounding the sixth-century church found new Byzantine structures to its north, west and south," wrote Dark and Kostenec in their book. Those structures include "traces of the white marble courtyard that once surrounded the sixth-century cathedral."

The researchers also identified what may be an ancient library located underneath a structure known as the large hall. Based on its size, that library could have held thousands of scrolls, Dark and Kostenec wrote. 

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