Medieval Christian-Muslim division was mental rather than geographical

Evidence

The physical frontier was not very clearly marked and was easily crossed. The frontier that divided the mental attitudes of Christians and Muslims was emphatically defined and crossed only with the greatest difficulty. — Norman Daniel, Islam and the West, 267

Categorization

• XREF: Connects to the reader’s work on decorum and moral boundaries — the idea that real frontiers in interfaith encounter are mental, not physical. — connects to: By 1250 the unity-of-God doctrine was common Christian knowledge about Islam; The medieval Christian-Muslim divide parallels modern Cold War ideological divisions.
• CANDY: A punchy, memorable two-sentence contrast worth sharing.