diff --git a/puzzles.but b/puzzles.but
index 9791ead..d56d26c 100644
--- a/puzzles.but
+++ b/puzzles.but
@@ -601,7 +601,8 @@ respectively.
 \cfg{winhelp-topic}{games.fifteen}
 
 The old ones are the best: this is the good old \q{\i{15-puzzle}}
-with sliding tiles. You have a 4\by\.4 square grid; 15 squares
+with sliding tiles, which dates from the 1870s.
+You have a 4\by\.4 square grid; 15 squares
 contain numbered tiles, and the sixteenth is empty. Your move is to
 choose a tile next to the empty space, and slide it into the space.
 The aim is to end up with the tiles in numerical order, with the