The Rosetta Stone, discovered in 1799 served as a crucial breakthrough. It contained multiple language versions, including ancient Egyptian hieroglyphs, Demotic, and Greek. This allowed linguists, particularly Jean-François Champollion, to compare the texts and gradually identify the values and meanings of hieroglyphic signs.
Champollion utilized the bilingual and trilingual inscriptions found in temples and on monuments to analyze hieroglyphic texts and understand their grammar and syntax.
The Book of the Dead, a collection of ancient Egyptian funerary texts, did contribute valuable information to the understanding of hieroglyphs. Still, it was not the only or primary resource for deciphering the entire hieroglyphic system. Champollion's examination of the Rosetta Stone and other inscriptions was paramount in unlocking the secrets of ancient Egyptian writing.