Thousands of Egyptians have demanded the return of the Rosetta Stone from the British Museum.The bilingual carvings on the relic proved to be the breakthrough in the decipherment of ancient Egyptian hieroglyphics after being unearthed by colonialists in Egypt in 1799.The stone is the centrepiece of a new exhibition at London's largest museum, celebrating the 200th anniversary of the stone's decipherment.The Rosetta Stone is one of more than 100,000 Egyptian and Sudanese relics housed in the British Museum. The London establishment says it obtained the stone lawfully.