"The carrier jumped again. It emerged in a secret vault below the Babylon where Hammurabi still reigned.
"The director of the base met the anthropologists and invited them to dine."
-Poul Anderson, The Shield Of Time (New York, 1991), p. 282.
The base, of course, belongs to the Time Patrol and their Babylon base is concealed from the Babylonians.
"He arranged for his guests to tour the city, properly disguised and under close guidance." (ibid.)
Not only disguised but also guided/guarded. Babylon would not have been a place where strangers could walk around unchallenged.
Another time traveler rides into the city:
"The city she approached was not yet the Babylon of the Bible, the city rebuilt by Nebuchadrezzar and the site of the captivity of the Jews, that would not be - would not have been - for another six centuries. The current Babylon was mostly not the city of Hammurabi the Lawgiver, sacked by the Hittites and refurbished by King Shuriash's ancestors. The Kassite kings dwelt more in their citadel of Dur-Kurigalzu a little to the west, but Babylon remained the greatest of their cities and the symbol of holiness and kingship in the land."
-SM Stirling, Against The Tide Of Years (New York, 1999), Chapter Twenty-One, p. 323.
the Patrol base is in 1765 BC in a timeline where it is imperative that the Jewish captivity occurs on schedule;
the Nantucketer approaches Babylon in 10 AE (= 1240 BC) in a timeline where the Jewish captivity will not occur.
It is time for another comparison with Neil Gaiman. When Morpheus visits a retired deity, he reminds him that they drank wine together in Babylon.
If anyone knows of a greater pleasure than writing about Anderson, Stirling and Gaiman, I would be pleased to hear about it. (I am talking about intellectual and aesthetic pleasures, of course.)