What is Poseidon’s Fountain?

Near the start of the book, Percy finds that there’s a magical fountain in his room from his father. The bottom of the fountain is filled with gold coins, which Percy can use to create an Iris message. The fountain represents Percy’s connection to his family, both divine and mortal. Every time he uses the fountain, he thinks about his family, and ultimately only uses it to contact his mother as well as his half-brother, Tyson. Percy even thinks to himself that Poseidon specifically gave it to him so he’d remember the links that he’s made with his family.