The Sabaean or Sabaic alphabet is one of the south Arabian alphabets. The oldest known inscriptions in this alphabet date from about 500 BC. Its origins are not known, though one theory is that it developed from the Byblos alphabet. The Sabaean alphabet, like Arabic and Hebrew, includes only consonants. Unlike Arabic and Hebrew, Sabaean has no system for vowel indication. In most inscriptions it is written from right to left, in some it is written in boustrophedon style (alternating right to left and left to right). It was used to write Sabaean, an extinct Semitic language spoken in Saba, the biblical Sheba, in southwestern Arabia. The Sabaeans managed to unite southern Arabia into a single state by the 3rd century AD, but were conquered by the Abyssinians in 525 AD.