Here’s what you’ll learn when you read this story:

• Research into a 10^th century medieval church rotunda in Poland looked to answer an unusual question: why didn’t it have a door?
• A university archaeologist believes she found evidence of a palace connected to the church.
• An internal staircase from the rotunda to the palace may have provided the connection people needed to get inside.

The rotunda of the Holy Virgin Mary church in Krakow, Poland may be relatively small at just about 32 feet across, but size isn’t its main peculiarity. Built in the 10th century, it’s one of the oldest stone churches in Poland—and it has no door. It was built with windows, but not a single door, and that’s puzzled researchers for decades.

In a new study published in the International Journal of Conservation Science by Klaudia Stala, an associate professor and archaeologist at Poland’s Krakow University of Technology, proposed a simple explanation for the conundrum: the church was part of a larger royal palace.

Using ground-penetrating radar, thermal imaging, and architectural analysis (the site is protected and prohibits excavation), Stala found evidence of a rectangular building next to and connected to the rotunda’s surviving walls. Stala theorizes that this neighboring structure was a royal palace, and that it was connected to the church by an internal passageway, with a staircase from the western gallery of the rotunda to the nave.

By removing the idea of the rotunda as a free-standing structure and rather making it part of a palatial complex that served as a palace chapel, Stala wrote that her theory “solves the problem of the lack of communication from the outside.”

The staircase theory isn’t fully new. But it is different. Previously, the most widely accepted explanation for how people entered the church was an external staircase that led to a door on a hypothetical second floor. But the remains of the church only stand about 20 feet high today and nobody’s quite sure the structure went much higher than that 1,000 years ago. Stala argues against the second-floor theory by pointing out that the church’s walls were relatively thin sandstone slabs bonded with pure-lime mortar. Those three-foot-thick slabs weren’t strong enough to handle the weight of additional floors. Plus, nobody’s ever found architectural evidence of an external staircase.

By having an internal staircase leading to the western gallery and then into a residential building, Stala concluded there’s no need for a second story. More importantly, there’s also no need for an exterior door.

Previous theories about the church suggested that it possessed a crypt on a buried first floor, further supporting the concept of an exterior staircase to the second floor, since sunken crypts would have only been accessible from inside the church. The unusually placed windows on the rotunda have previously been used to support the crypt theory, since the windows’ location suggests that the ground level was once much higher.

Stala’s thermal imaging scans found no evidence of a crypt at the four-apsed Church of the Holy Virgin Mary on Wawel Hill. She argues that the building’s low-set windows and overall architectural style don’t require the presence of a buried lower level, pointing to similar small, round churches in Croatia and Italy that share these features don’t contain any crypts. Ground-penetrating radar surveys near the rotunda revealed underground anomalies consistent with the outline of a large rectangular building oriented crosswise to the church, a layout that closely matches other early medieval Polish palace complexes, most notably the recently excavated royal compound at Ostrów Tumski in Poznań.

Taken together, Stala concludes that the rotunda most likely served as a palace chapel, directly linked to a royal residence and accessed through an interior passage rather than an exterior door. The reason no entrance has ever been found in the church's walls, even where they survive to heights of more than six meters? According to her research, one was never needed.