Scotland a territorial parish structure, with every community in Scotland having a local congregation. Scotland also has a significant Roman Catholic population, 19% professing that faith, particularly in Greater Glasgow and the north-west. After the Reformation, Roman Catholicism in Scotland continued in the Highlands and some western islands like Uist and Barra, and it was strengthened during the 19th century by immigration from Ireland. Other Christian denominations in Scotland include the Free Church of Scotland, and various other Presbyterian offshoots. Scotland's third largest church is the Scottish Episcopal Church. Islam is the largest non-Christian religion (estimated at around 75,000, which is
Demography of Scotland Fife indicate that arable land spread at the expense of forest from about 2000 BC until the period of the first century AD Roman advance into lowland Scotland, suggesting an expanding settled population. Thereafter, there was re-growth of birch, oak and hazel for a period of five centuries, suggesting that the Roman invasions had a negative impact on the native population. There are almost no written sources from which to re-construct the demography of early medieval Scotland. Estimates have been made of a population of 10,000 inhabitants in Dál Riata and 80-100,000 for Pictland, which was probably the largest region.