Christianity was introduced into the area from Ireland in the latter half of the 6th century AD. There are many sites associated with early Christian activity, many of them including the placename elements Cille or Kil and Annat. St Maelrubha founded a monastery at Applecross in 673 AD. His grave is supposed to be marked by the Red Priest's stone in Strathnaver, although this is disputed. The early Tarbat monastery at Portmahomack in Easter Ross has been excavated over the last few years by York University, who have found evidence of a range of craft activities including making parchment for manuscripts.
Viking raids began at the end of the 8th century, and it seems likely that Tarbat was burned down. The Vikings arrived from Norway by way of Shetland and Orkney, and they soon began to settle many coastal areas. Caithness, the coastal areas of Sutherland and Wester Ross, and the Hebrides all came under Norse control as can be seen from many surviving placenames. The Hebrides transferred from the Kingdom of Norway to the Kingdom of Scotland after the battle of Largs in 1266, but Orkney and Shetland did not become part of Scotland for another 200 years. Even today the Caithness dialect shows Scandinavian influences. Dingwall was the Thing-vollr, the local Norse parliament, as survives today in the Isle of Man's Tynwald.
The Highlands lay on the great trading seaway from Scandinavia to Ireland, France and Spain, and at Smoo Cave (Sutherland) boat fittings have been found where ships have put in to refit before or after rounding Cape Wrath. Today however there are few Norse archaeological sites that can be visited in Highland. In Caithness there are the remains of extensive settlements hidden beneath sand-dunes, and Old St Peter's Church in Thurso has a runic stone built into its wall. Near Thurso can be seen the remains of the Castle of the Norse Bishops at Scrabster and near Wick is the square stone tower of the Castle of AuldWick. Many local chiefs seem to have continued to occupy Iron Age forts.
The later middle ages, from about 1200 to about 1550 AD, were dominated by the attempts of the kings of Scotland to establish their power over the Highlands, including the Earldom of Orkney in Caithness and Sutherland, and the Lordship of the Isles in the west. The Lords of the Isles were the successors to the largely independent kingdom of Man and the Isles. In an attempt to divide and rule, chief was set against chief. The insecurity of the times encouraged the growth of the clan system. There are still many castles surviving from this period built by clan chiefs: on Skye alone there are Duntulm, Dunvegan, Brochel, Knock, Dun Sgathaich and Castle Maol. Anglo-Norman lords such as the De Morays in Sutherland and the St.Clairs (Sinclairs) in Caithness were granted estates in the area, and they too established castles. Alexander Stewart, the 'Wolf of Badenoch' had his at Ruthven, where fragments of wall can still be seen beneath the 18th century barracks. Towns such as Inverness were also established as centres of trade and royal power. These burghs were however confined to the east, around the Moray Firth - there do not seem to have been any foundations in the west.
King James IV repeatedly visited the shrine of St Duthac at Tain in the early 16th century, combining pilgrimage with political expediency. Medieval kings could made use of church organisation to help them establish control in their territories. The bishopric of Ross was established by the 12th century with its centre initially in Rosemarkie, then later at Fortrose Cathedral.
However in much of the Highlands it was also a time of flourishing Gaelic culture and learning, with extensive links to Ireland, the Isle of Man, and continental Europe. Medical science, music, poetry and art all received patronage from clan chiefs. St Columba's Isle, near Skeabost on Skye was the cathedral of the Bishops of Sodor (i.e. Sudreyar, the Norse Southern Isles) and Man until they moved to Iona in 1499.
Apart from castles and the remains of a few churches, there is little later medieval archaeology that can be seen today. Most houses seem to have been built using wood, peat, and thatch and most household items were also made of organic materials. Everything was recycled. However it seems very likely that many remains of deserted villages dating to the 18th and 19th centuries are sitting on top of earlier houses and fields: once you have cleared the stones from the land in the Highlands, why move unless you have to?