Hospitality suggests a generosity of spirit and a full-throated welcome. The hospitable soul not only welcomes visitors but celebrates their arrival. They are curious about where the traveler hails from and where they will be going. They must trust the visitor and be trusted by them in turn.

In ancient Greece, xenia was the term for this relationship between host and guest and the concept was a cornerstone of the culture. So crucial was xenia to the Greeks that it was the domain of Zeus, the king of the gods—and the protector of strangers. In myths, Zeus zealously watched over how hosts treated guests and how guests showed them gratitude. The Greeks believed that it would offend Zeus himself if welcome was denied to a stranger that turned up on your doorstep.

Great wars in ancient l...