1)
What is "Sheshach"?
1.
Rashi: It is Bavel, in At-Bash (we exchange the first, second, third... letters of the Aleph Beis with the first, second... letters from the end).
2)
Why is the capture and desolation of Bavel so surprising?
1.
Malbim: All nations came to Bavel for business, and they were submissive under it.
