Egyptian hieroglyphic writing was developed about 3100 bc and continued in use with remarkably little change until the 4th century ad. Its meaning seems to have been forgotten soon afterwards and the hieroglyphs were not deciphered until early in the 19th century following the discovery of the bilingual inscription known as the Rosetta Stone. Some 700 signs were employed. The majority of these are ideograms: simplified pictorial representations of the concepts to which their meaning relates. Some of these ideograms also had a phonetic value representing one or more consonants. Vowels were not indicated, so it is often not possible (other than by comparison with related Coptic words) to ascertain the original pronunciation. Ideograms and phonetic symbols were generally combined, for example the word ‘depet’, meaning a boat, could be written Inscriptions were generally written from right to left, but also on occasion from left to right or vertically. Gaps between words were not indicated. Royal names were enclosed in an oval line or cartouche. Less formal scripts, the so-called hieratic and demotic, were also used and may be traced back to the Fifth Dynasty.