Help: Detroit Paving History

[SFDS]

A friend has a small terraced backyard in Detroit. He was told decades ago the terraces were built from old Michigan Ave debris. They are not the red bricks many of us know, but rather the underlying cement. He has also unearthed 5 of the numbered "Block" plates in his backyard. Perhaps these plates were buried guiding the road construction? Or for some other purpose?

[Burnsie]

I'd guess that the blocks with the numbers on them identify the block number of a given plat, and were placed on the curb or sidewalk. Something that decorative would have been placed above ground and intended to be permanent.