It refers to the location and it's story. The first christian community of monks and some of the first hermits went there to live in meditation and pray. Paolo Uccello shows how he thinks life should be there at the time.

I think it was in ancient Egypt, not far from where now is Sudan. I only know for sure that it was a desert place. Not in Greece, as far as I know (but I must admitt it's not my field)