Who Can Tell Me Why?

I acquired a spalted maple log from a local tree service this past summer, little did I know I would be in for a series of surprises. Once home I was anxious to open it up to reveal the spalting that I could see on the ends of the log but hit something hard with the chainsaw right in the middle of the tree. Once I got my damaged blade replaced I carefully finished cutting the log in half and this fell out….

I could see there was more so I decided to saw the log in half lengthwise…

Now I’m puzzled…I’m looking at old concrete individual stacked bricks with nails embedded in them and the tree had completely formed around them.

What purpose did these bricks serve? Who put them there? How did they stay in place as the tree grew? How did they end up smack dab in the middle of this tree? I’m usually good for a theory or two but this one has me stumped!
What I do know is the mixture of dead and live wood in addition to the spalting has made for a spectacular finished piece of work.

Any ideas?