Anthony and Cleopatra

One of the gaurds at a roman estate found anthony and cleopatra dead a few feet away from each othe at the end of the day. He immediately called Ceasar who confirmed that they were both dead. Caesar ruled out poison and there was no sign of foul play. He did seee a small crack that in the floor, which ran between the two bodies, and concluded that the crack is what caused their death. He was right but how did they die?

Clues:
they had not been strangled or suffocated.
they were both naked
they were both good swimmers
they did not injure themselves by diving into an empty bath or swimming pool

(from the book Lateral Thinking.... we were laughing at how dopey some of these puzzle are so we thought we should share one with you!)