distance and time but also history:
"...the Aramaeans were slated to overrun most of the Middle East in the dark age that the pre-Event histories said was coming, and their tongue and ways would stamp themselves on the region for millennia. Aramaic would be the state language of the Persian Empire, and the native tongue of Jesus. Or would have been..."
-SM Stirling, Against The Tide Of Years (New York, 1999), Chapter Fifteen, p. 229.
I knew that Jesus spoke Aramaic but not that the Persians did also. The Persian Emperors start with Cyrus who is prominent both in the Bible and in Poul Anderson's Time Patrol series. Without Cyrus, there would have been no Return from Exile and therefore no Christianity. This makes Cyrus a divine agent in the Bible and a pivotal figure for the Patrol. In SM Stirling's Nantucket timeline, none of that is going to happen...
I said recently that, when discussing time travel, the Time Patrol series is an endless source of comparisons and quotations. Here we are again, as the bishop said to the actress. Time Patrol is like a Bible of time travel. On the map of Cyrus' Empire (see image), we recognize Bactria from the sequel to Time Patrol, The Shield Of Time. Everard reminds Dennison/Cyrus that most of Alexander's conquests consisted of taking over Persian territory. Everard is in Bactria after Alexander's generals have divided his empire up between them.
Note: See comments.