A parallel text is a text placed alongside its translation or translations. Parallel text alignment is the identification of the corresponding sentences in both halves of the parallel text. The Loeb Classical Library and the Clay Sanskrit Library are two examples of dual-language series of texts. Reference Bibles may contain the original languages and a translation, or several translations by themselves, for ease of comparison and study; Origen's Hexapla placed six versions of the Old Testament side by side. A famous example is the Rosetta Stone, whose discovery allowed the Ancient Egyptian language to begin being deciphered.

The writing systems used in ancient Egypt were deciphered in the early nineteenth century through the work of several European scholars, especially Jean-François Champollion and Thomas Young. Ancient Egyptian forms of writing, which included the hieroglyphic, hieratic and demotic scripts, ceased to be understood in the fourth and fifth centuries AD, as the Coptic alphabet was increasingly used in their place. Later generations' knowledge of the older scripts was based on the work of Greek and Roman authors whose understanding was faulty. It was thus widely believed that Egyptian scripts were exclusively ideographic, representing ideas rather than sounds, and even that hieroglyphs were an esoteric, mystical script rather than a means of recording a spoken language. Some attempts at decipherment by Islamic and European scholars in the Middle Ages and early modern times acknowledged the script might have a phonetic component, but perception of hieroglyphs as purely ideographic hampered efforts to understand them as late as the eighteenth century.