Scottish Gaelic itself developed after the 12th century, along with the other modern Goidelic languages. Scottish Gaelic and its predecessors became the language of the majority of Scotland after it replaced Cumbric, Pictish and in considerable areas Old English.^[17] There is no definitive date indicating how long Gaelic has been spoken in today's Scotland, though it has been proposed that it was spoken in its ancient form in Argyll before the Roman period^[18]. No consensus has been reached on this question; however, the consolidation of the kingdom of Dál Riata around the 4th century, linking the ancient province of Ulster in the north of Ireland and western Scotland, accelerated the expansion of the language, as did the success of the Gaelic-speaking church establishment, started by St Columba, and place-name evidence shows that Gaelic was spoken in the Rhinns of Galloway by the 5th or 6th century.^{[citation needed]} The language was maintained by the trade empire of the Lordship of the Isles, which continued to control parts of Ulster until the 1500s.

[edit] From the Middle Ages to the end of Classical Gaelic education

The Gaelic language eventually displaced Pictish north of the River Forth, and until the late 15th century was known in the Scots' English language as Scottis, and in England as Scottish. Gaelic began to decline in mainland Scotland from the beginning of the 13th century, accompanying its decline in its status as a national language, and by the beginning of the 15th century, the highland-lowland line was beginning to emerge.^{[citation needed]}