The tablet was over 30,000 years old before it was discovered. The writing on it was written in Bajoran ideograms. The first part of the tablet that was easily decipherable were two symbols that said: "Welcome, Emmisary".
Seeing this message, Starfleet Captain and Emissary Benjamin Sisko took the tablet to Deep Space 9 to ascertain its meaning. During this time, Sisko then had an urge to break it, unleashing a Prophet and a Pah-wraith. The two beings then fought each other until Kai Winn ended it. (DS9 episode: "The Reckoning")