Basilica of Saint Sabina

This guide to the Basilica of Saint Sabina on Rome's Aventine Hill starts at a small opening in the courtyard wall, framing a gnarled orange tree said to date to 1220, when the Spanish friar Dominic arrived here at the pope's invitation with almost nothing but a seed from home. It jumps forward more than a century and a half to Catherine of Siena, who picked fruit from that same tree to carry to Pope Urban the Sixth during a bitter crisis in the church. Peer through the oval opening before you step inside, and see whether the tree is in fruit.