"Mark Twain's Memory-Builder" (patented 1885) [prototype boards & other game artifacts, including cribbage board and pins, 1880s]
Clemens explained the game's origin in a letter of 20 July 1883 to his friend Joseph H. Twichell:
Day before yesterday, feeling not in condition for writing … I spent eight hours in the sun with a yard-stick measuring off the reigns of the English kings on the roads in these grounds, from William the Conqueror to 1883—calculating to invent an open-air game which shall fill the children's heads with dates without study.… I did a full day's work & a third over, yesterday, but was full of my game after I went to bed,—trying to fit it for indoors. So I didn’t get to sleep till pretty late; but when I did go off, I had contrived a way to play my history game with cards & a cribbage board.