Irish rish, or Irish Gaelic, is the oldest of the Goidelic group of Celtic languages. Ancient written examples exist in the ogham inscriptions, on about 370 gravestones scattered through southwestern Ireland and Wales. Dating from the 5th to the 8th century, the inscriptions consist almost entirely of proper names. Irish can be grouped into four periods: Old (circa 800-1000 CE), Early or Early Middle (1200-1500 CE), Middle (1200-1500 CE), and Modern (from 1500 CE). Originally a highly inflected language, Irish retains essentially two noun cases, nominative and genitive, with the dative surviving in the singular of feminine nouns; the language has only two verb tenses in the indicative mood. It is chiefly spoken in the western and southwestern parts of the Republic of Ireland, where it is an official language, and to some extent in Northern Ireland. In the past century, the number of Irish-speaking persons has declined from 50 percent of the population of Ireland to less than 20 percent. Scottish Gaelic A form of Gaelic was brought to Scotland by Irish invaders about the 5th century, where it replaced an older Brythonic language. By the 15th century, with the accretion of Norse and English loanwords, the Scottish branch differed significantly enough from the Irish to warrant definition as a separate language. The alphabet of Irish and Scottish Gaelic is identical, consisting of 18 letters. Scottish Gaelic employs four cases of nouns: nominative, genitive, dative, and vocative. Like Irish, the accent is on the initial syllable. Scottish Gaelic exists in two main dialects, Northern and Southern, roughly geographically determined by a line up the Firth of Lorne to the town of Ballachulish and then across to the Grampian Mountains, which it follows. The Southern dialect is more akin to Irish than is the Northern, and is more inflected. The main difference is the change of the é sound, which is eu in Northern dialect and ia in Southern. Thus, the word for "grass" is pronounced feur in Northern and fiar in Southern. Scottish Gaelic also has a few thousand speakers in Nova Scotia. Manx The language of the Isle of Man is classed as a dialect of Scottish Gaelic, with strong Norse influence. It began to decline in the 19th century, and in the early 20th century it became virtually extinct. The first written records are of the 17th century, and Manx literature, apart from ballads and carols, is negligible. Celtic Index