These pretty flowers are common mallow.
I have been familiar with mallows since my childhood,
although it was only recently that I learned the name 'mallow':
to me they were always "cheesies"
because the flower bud looked like a small round cheese
and could be eaten.
(In fact in my neighborhood they were widely eaten.)
Perhaps that's why I rarely saw them flower...
Ha, actually I saw lots of mallow flowers,
but in Utah, the flowers are tiny.
Now in Rome, under that hot mediterranean sun,
the mallow flowers are ginormous.
And growing everywhere at Ostia!