My small back yard was absolutely weed ridden so I've nuked it and I'm in the process of raking out all the dead, deeply rooted weeds and discovering all kinds of detritus in the dirt. Lots of stones, lumps of concrete, bits of metal, plastic, glass, more stones, large root systems, stones etc.

Anyway, this is one of the things I uncovered and I'm just curious as to what it is. Some kind of gardening or building aid I guess?