I was not certain of this is part of the wall (it certainly looks it), or a stash of the many rocks that must have been found during excavations. The latter was the4 case as I saw in 2015: The Wigand-dump, from 1896 and not, as many visitors think, an ancient construction. Ground that was excavated from the theatre was dumped here.
The dog belonged to one of several herd of goats that roamed the city. You will see some of them in the theatre, and when I compare older pictures with the fresh ones they seem to do a good job at keeping the grass at bay.