Season 23 aired between 11 Oct 2010 and 16 May 2011, 12 episodes.
Episodes
E01
God in America (Parts 1–2)
11 Oct 2010
E02
God in America (Parts 3-4)
12 Oct 2010
E03
God in America (Parts 5-6)
13 Oct 2010
E04
Robert E. Lee
03 Jan 2011
E05
Dinosaur Wars
17 Jan 2011
E06
Panama Canal
24 Jan 2011
E07
The Greely Expedition
31 Jan 2011
E08
Triangle Fire
28 Feb 2011
E09
The Great Famine
11 Apr 2011
E10
Stonewall Uprising
25 Apr 2011
E11
Soundtrack for a Revolution
09 May 2011
E12
Freedom Riders
16 May 2011