> Big cities require some attentiveness.
The size of the city isn't the issue here. There is definately a correlation between size and crime, but that's not the real issue - what it is I don't know though.
I live in a mid-sized European capital (bigger than Lisbon), and it's one of the safest places I've ever lived. I could probably leave my car running, with an expensive camera on the dash, while going to get a coffee, and everything would still be there when I get back.
Compare this to some Italian cities I've been to - which are smaller - where I feel lucky all four wheels are still there when getting back (locking wheel nuts are easy to break btw). I lived in Rome for a while and if you left something that even looked like it could contain valuables on show, you'd come back to a broken window.