diff --git a/README.md b/README.md
index 794fc4c..8752312 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,7 @@
 [Construct Your Own]: docs/construct_your_own.md
 [logo]: docs/images/logo.png
 [buy sets of puzzles]: https://www.thegamecrafter.com/designers/don-kirkby-s-games
+[Cross Jig Publishing Co.]: https://www.oldpuzzles.com/buy-puzzles/sale-list/crossword-puzzle-1
 
 ![logo]
 
@@ -32,6 +33,9 @@ Here's a small starter puzzle to see how they work. You can also print out the
 [PDF]. Find more challenging puzzles I've published on [Puzzling Stack Exchange].
 If you don't want to print and cut out your own, you can [buy sets of puzzles].
 
+I recently learned that I was not the first to build a crossword puzzle out of
+tetrominoes. The [Cross Jig Publishing Co.] published one in 1932.
+
 ## Greetings (7x7)
 Clue numbers are shuffled: 1 Across might not be the top left. 10 pieces.
 
diff --git a/docs/index.md b/docs/index.md
index 7cf6284..17601c7 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -10,6 +10,7 @@ subtitle: Crossword puzzles to assemble
 [Construct Your Own]: construct_your_own.md
 [logo]: images/logo.png
 [buy sets of puzzles]: https://www.thegamecrafter.com/designers/don-kirkby-s-games
+[Cross Jig Publishing Co.]: https://www.oldpuzzles.com/buy-puzzles/sale-list/crossword-puzzle-1
 
 ![logo]
 
@@ -23,6 +24,9 @@ Here's a small starter puzzle to see how they work. You can also print out the
 [PDF]. Find more challenging puzzles I've published on [Puzzling Stack Exchange].
 If you don't want to print and cut out your own, you can [buy sets of puzzles].
 
+I recently learned that I was not the first to build a crossword puzzle out of
+tetrominoes. The [Cross Jig Publishing Co.] published one in 1932.
+
 ## Greetings (7x7)
 Clue numbers are shuffled: 1 Across might not be the top left. 10 pieces.