150th anniversary of the letter's publication. Even when the Rosetta Stone was undergoing conservation measures in 1999, the work was done in the gallery so that it could remain visible to the public. Reading the Rosetta Stone Prior to the discovery of the Rosetta Stone and its eventual decipherment, the ancient Egyptian language and script had not been understood since shortly before the fall of the Roman Empire. The usage of the hieroglyphic script had become increasingly specialised even in the later Pharaonic period; by the 4th century AD, few Egyptians were capable of reading them. Monumental use of hieroglyphs ceased as temple priesthoods died out and Egypt was converted to Christianity; the last known inscription is dated to , found at Philae and known as the Graffito of Esmet-Akhom. The last demotic text, also from Philae, was written in 452. Hieroglyphs retained their pictorial appearance, and classical authors emphasised this aspect, in sharp contrast to the Greek and Roman alphabets. In the 5th century, the priest Horapollo wrote Hieroglyphica, an explanation of almost 200 glyphs. His work was believed to be authoritative, yet it was misleading in many ways, and this and other works were a lasting impediment to the understanding of Egyptian writing. Later attempts at decipherment were made by Arab historians in medieval Egypt during the 9th and 10th centuries. Dhul-Nun al-Misri and Ibn Wahshiyya were the first historians to study hieroglyphs, by comparing them to the contemporary Coptic language used by Coptic priests in their time. The study of hieroglyphs continued with fruitless attempts at decipherment by European scholars, notably Pierius Valerianus in the 16th century and Athanasius Kircher in the 17th. The discovery of the Rosetta Stone in 1799 provided critical missing information, gradually revealed by a succession of scholars, that eventually allowed Jean-François Champollion to solve the puzzle that Kircher had called the riddle of the Sphinx. Greek text The Greek text on the Rosetta Stone provided the starting point. Ancient Greek was widely known to scholars, but they were not familiar with details of its use in the Hellenistic period as a government language in Ptolemaic Egypt; large-scale discoveries of Greek papyri were a long way in the future. Thus, the earliest translations of the Greek text of the stone show the translators still struggling with the historical context and with administrative and religious jargon. Stephen Weston verbally presented an English translation of