Bottom line, to sightsee comfortably in Rome in May:
- Wear comfortable shoes/walking sandals.
- Dress in light cotton pants, capri pants or a long skirt.
- Wear a light cotton top.
- Bring a cardigan/pullover and/or a light jacket in your bag.
- Bring a light cotton scarf for men and women.
- Don't forget your sunscreen and sunglasses!