Photo by Américo Cardoso (2010)
This is also called the Alcobertas Dolmen. This is not an in-place dolmen as a quick visual inspection shows because it is circular instead of rectangular, and the stones are leaning inwards instead of being free standing with deep roots. The stones have been moved here from elsewhere.
The legends surrounding these stones tell of a similar tale of movement.
Faithful Christians dismantled the dolmen because it was a pagan symbol, but by divine powers it was rebuilt by Mary Magdalene. Every time the people destroyed the dolmen the saint rebuilt it. Consequently, the people decided to place its stones next to their chapel they wanted to build.
It was Santa Maria Madalena who transported the stones from Serra da Lua (neighboring mountain) and placed them in this place to form a place of prayer for the people.
The Saint gave birth to the stones in this place so that believers could atone for their sins.
Blog by Américo Cardoso
https://rio-maior-cidadania.blogspot.com/2010/02/dolmen-igreja-de-santa-maria-madalena.html