Final answer:
The Upper Church in the Basilica of San Francesco in Assisi features a single long nave designed for large gatherings, with a double surround of columns, and side chapels for veneration without disturbing mass.
Step-by-step explanation:
The interior of the Upper Church in the Basilica of San Francesco, Assisi, is characterized by architectural elements typical of the basilica plan, which is designed to accommodate large numbers of pilgrims.
The nave, being the main hall, is neither just a simple hall before descending to a church below nor a small chapel dedicated to Francis. Instead, it is a single long nave with no side aisles but with three chapels on both sides, having lower barrel vaults. These chapels allowed pilgrims to venerate relics without disturbing the mass.
The interior also features a double surround of columns that support the structure. These design choices are apt for managing large crowds that the pilgrimage church would have hosted, providing both a central space for congregation and circulation paths for the movement of people.