What's the dress code for churches in Italy?

Shoulders and knees covered, for everyone. It's enforced at St Peter's, the Duomo in Florence, St Mark's in Venice and many smaller churches, and enforcement means being turned away at the door after queuing. No tank tops, no shorts above the knee, no bare shoulders — this applies to men too, which surprises people. The easy solution in summer is a light scarf or shawl in your bag to throw over shoulders, and trousers or a longer skirt rather than shorts on days you're visiting churches. Hats come off inside. Some churches also ban photography, and a few ban talking above a murmur.