The Rosetta Stones, known as Sacred Stones of Power in the NES version, are key items that appear in Double Dragon 3: The Rosetta Stone and its home console version, Double Dragon III: The Sacred Stones. They are three magical gems, each of a different color, said to yield an immeasurable amount of power –enough to conquer the world– to those who possesses them all.
Three of them are known to exist (with a fourth later revealed to exist in the NES/Famicom version), which are scattered around the world and each in possession of a powerful adversary the heroes will have to defeat first in order to claim them. The Lee brothers spend the first four missions searching for these magical stones before traveling to Egypt and using them to uncover an ancient treasure.
In the arcade version, the first stone is found in China, held by a powerful Kung Fu master known as Li Cheng-Long. The second stone is found in Japan, in possession of a skillful ninja master known as Yagyu Ranzou.
The third stone's whereabouts is somewhat left to ambiguity, as the game's limited storytelling (both textually and graphically) isn't clear if it was in Hiruko's possession all along (as it happens with the fourth stone in the NES/Famicom version), and/or if there was a fourth stone that altogether allowed safe passage into Cleopatra's burial chamber, where four stones can in fact be seen encrusted on golden tablets on the chamber's walls (although these could merely be design aesthetics and actually be unrelated to the Rosetta Stones). To add to the confusion, the English ending text says that "when the third stone is found, its power will change the world", implying that they never found the third stone and probably that's why they were attacked inside the pyramid in the first place. The original Japanese ending, on the other hand, says that "when all three stones become one, their power will change the world".
Whatever the case is, the stones give access to Cleopatra's burial chamber and also to her treasury, which the heroes claim possession of and later give to charity.
Similar to the arcade version, the first stone is once again found in China, although now held by a powerful Chinese warrior known as Chin Seimei, who happens to be none other than Chin Taimei's brother (an adversary from the first game) and who is seeking revenge on the Lee brothers for his supposed death at their hands.
After collecting this stone, Hiruko reappears and confesses that she had been in possession of the third stone all along, and so she sets the heroes on their way to Egypt, where they are to meet the ultimate adversary (or find Marion in the NES version).
After traversing many perilous traps inside the great pyramid, the heroes finally reach the door to Cleopatra/Princess Noiram's burial chamber (or supposedly where Marion is kept hostage). At this moment, Hiruko suddenly shows up and reveals her true intentions, making haste in entering the chamber while holding the three Rosetta Stones in her thirst to claim the secret power held within the pyramid and with it conquer the world. Unfortunately for her, she was unaware of the entire legend of the Sacred Stones of Power, which said:
carrying less than all four stones
will be turned to dust."
And so, not knowing of the existence of a fourth stone, she enters the burial chamber while holding only three of them, only to exit a few seconds later and, as the legend predicted, turning into dust.