Conversation so far:
who played the mermaids in pirates of the caribbean
Àstrid Bergès-Frisbey and Gemma Ward play the mermaids in Pirates of the Caribbean: On Stranger Tides.
who directed the movie Pirates of the Caribbean: On Stranger Tides?
Rob Marshall directed Pirates of the Caribbean: On Stranger Tides.
who produced the movie Pirates of the Caribbean: On Stranger Tides?
Jerry Bruckheimer produced Pirates of the Caribbean: On Stranger Tides.

Question: what was the movie based on?
Self-contained rewrite: what was the movie Pirates of the Caribbean: On Stranger Tides based on?