MEXICO CITY — Indigenous symbols like a feather headdress, an axe and a shield have been found under layers of lime plaster at open-air chapels in a convent just south of Mexico City, experts announced Monday.

The finds suggest Spanish priests not only altered their church architecture to accommodate the large number of Indigenous converts, but also allowed masons to paint pre-Hispanic designs on the walls.

The convent in the town of Tepoztlan dates back to the 1500s, when Spanish Catholic priests built open-air church patios to teach and convert Indigenous groups after the 1521 conquest of Mexico.

Indigenous peoples in Mexico were accustomed to holding religious ceremonies in the open air, as is done in many pre-Hispanic cultures, and were reportedly distrustful of large, roofed spaces like churches.

To attract them, the priests built open-air chapels: A small arched vestibule for officiating the Mass, facing a large open patio surrounded by the four walls of the church patio.

The National Institute of Anthropology and History said the paintings were found in three smaller structures known as “Posing Chapels,” built in the four corners of the open patio. In Tepoztlan, the fourth chapel had collapsed long ago.

Often found in conjunction with open chapels, the “posing chapels” held statues of saints used to mark processions and teach converts.

Restoration experts were cleaning and stabilizing large, one-yard (meter) diameter painted red circles on the walls. Those kind of circles can be seen elsewhere in the convent, filled with Christian imagery.

But they were surprised when they cleaned off centuries of dirt, plaster and paint to find the symbols contained pre-Hispanic symbols like the headdress, flowers, axe and a shield.

The Institute said in a statement it was researching whether the symbols referred to Tepoztécatl or some other Indigenous god.

The four corner chapels were also sometimes associated with particular neighborhoods into which towns were divided.