So last night I started digging a hole in which to plant my hydrangea. Along with an incredible assortment of broken bottles, window panes, metal objects, parts of toys, and other debris, eventually I dug this out.
The handle broke off underground; it was about 12" deep. Concrete part is about 24" wide and 18" thick.
Here's it's shown with the two metal anchor roots facing up (inverted from its buried position).
When I moved in, there was something similar (a metal loop) embedded in the concrete near the corner of the garage, near the door. (It's long gone, as I didn't need a tripping hazard.) Locations scribbled in yellow.
House was built in the 1890s, the garage later. Going by the two handles, the installation would have been no earlier than 1970. The guys who cut the first one off at the cement suggested that this was used to hold a pulley or jack, and that someone had been lifting engines out.
Any other ideas? (I know that this will go to whimsey pretty soon; I would appreciate real-life guesses first.)