Guard Stones in Vienna
Vienna has a lot of guard stones, as do probably all old European cities and towns. Most that I found were made of stone, but I also found some metal ones. In the medieval center stone is more common, while metal barriers are common for newer buildings.
Looks as though these were cut in half.
The shape of these is similar to ones I've seen in Lviv
Interestingly, these are to protect a tree.