Filling in a hole

I was working in a warehouse and sweeping the floor.  I used sawdust to see where I had swept so far.  I swept up a huge pile of dirt, mostly hair.  I took the dirt outside the building to empty.  There was a doorway that was below ground level.  The doorway had a large hole around it so it was visible from the surface of the ground.  The hole was a semicircle and lined with large square rocks.  I started filling in the hole by tipping the rocks into the hole.  The rocks were very heave but with a lever I was able to tip them in.  Every rock that went into the hole lined up perfectly so there was no gaps and the rocks laid flat instead of being all jumbled up.  One of the rocks did not go perfectly in place and I had to nudge it in its place just a little bit.