- Arrigucci, Caterina1
- Arrigucci, Luigi1
- Artedo, Petrus de1
- Asceticism--Early church1
- Assumption of the Blessed Virgin Mary1
- Astrology, Arab1
- Astronomical instruments1
- Astronomy, Arab1
- Astronomy, Greek1
- Attila, -4531
- Augsburg Confession1
- Aurispa, Giovanni, approximately 1376-14591
- Austria--Lambach (Upper Austria)1
- Banks and banking1
- Baptism1
- Baptism of Jesus Christ1
- Baptism--Catholic Church1
- Barbara, Saint1
- Bardi, Giovanni de', conte di Vernio, 1534-16121
- Basilica di S. Marco Evangelista al Campidoglio (Rome, Italy)1