The Saint-Clairs were Normans, and came over to England with William the Conqueror. Richard of Saint-Clair and Brittel of Saint-Clair are both mentioned in Domesday Book. William of Saint-Clair witnessed a charter granted by King Stephen in 1135.
Saint-Clair was originally the name of a place. The proprietor of it and the members of his family designated themselves as being de Sancto-Claro, or of Saint-Clair. In course of time the de, or of, was dropped, and Sanctus-Clarus, or Saint-Clair, adopted as a surname. Through the wear and tear of language Saintclair has, as a general rule, been changed to Sinclair.
About the year 1160 Henry of Saint-Clair obtained a charter of the lands of Herdmanston in Haddingtonshire. Henry is the first Sinclair with whom we meet in Scotland. It is certain, however, that he was not the first of the name who settled in that country. His descendants are still in possession of Herdmanston.
Roslin, or Roslyn, is a Gaelic word, and means ros linne, or the promontory of the pool. The place known by this name is about eight miles from Edinburgh.
Willielmus de Sancto Claro, Miles, or William St.Clair, Knight, received in 1280 a charter of the lands and barony of Roslin. This William was the progenitor of the St.Clairs of Roslin and the Sinclairs of Caithness. He was succeeded by his son, Sir Henry. Sir William, son of Sir Henry, was killed in Spain in 1330. Sir William, son of Sir William, succeeded his grandfather in Roslin. He married Isabel, daughter of Malise, the Keltic Karl of Stratherne, Caithness, and Orkney, and had by her one son, Sir Henry, fourth of Roslin.
Author's Addition (2nd Edition 1902):
The first six earls of Strathern were undoubtedly Kelts. It is possible, however, that Malise, the 7th earl, belonged to a different family by his father. Be that as it may, he married Marjory, daughter of Hugh, Earl of Ross, who was a thorough Kelt, and had by her Isabel. Sir William St.Clair, third of Roslin, married Isabel and had by her Henry, the first Sinclair earl of Orkney. A book published at Venice in 1558 asserts that the latter made a voyage to America.
Sir Henry claimed the Earldom of Orkney through his mother, and received it from Haco, King of Norway, in 1379. He was Admiral of Scotland. He died in 1404 and was succeeded by his son, Henry.
Sir Henry, fifth Baron of Roslin and second Earl of Orkney, succeeded his father as Admiral of Scotland. He was created Lord Sinclair in the Scottish peerage. He married Egidia, daughter of Sir William Douglas of Nithsdale the Black Douglas of history and had by her two children, William and Beatrix. He died in 1420, and was succeeded by his son.
Beatrix, his daughter was married to James, seventh Earl of Douglas. She was the mother of William, eighth Earl of Douglas, of James, ninth Earl of Douglas, of Archibald, Earl of Moray, and of Hugh, Earl of Ormand.
Author's Addition (2nd Edition 1902):
Walter, sixth High Steward of Scotland, married Marjory, daughter of Robert Bruce, by whom he had one son, Robert. Robert became King of Scotland, and was the first of the old Stewarts. The Black Douglas married his daughter Egidia and had by her Egidia, wife of Henry St.Clair, second Earl of Orkney. William St.Clair, first Earl of Caithness, was thus descended from the Black Douglas and King Robert Bruce.
William St.Clair, sixth Baron of Roslin, third Earl of Orkney, and second Lord Sinclair, possessed immense estates, and lived at Roslin Castle in a style of the greatest magnificence. He was Admiral of Scotland in 1436, and High-Chancellor in 1454. He received a grant of the earldom of Caithness, August 1455. He married, first, Elizabeth, daughter of Archibald, Earl of Douglas, and had by her one son, William the Waster. He married secondly, Marjory Sutherland, by whom he had Oliver, William, and other sons. He was deprived of the Earldom of Orkney by James III in 1471. He received as some compensation the lands of Ravenscraig in Fife.
He divided his possessions, in 1476, among his three eldest sons. He gave the lands of Newburgh in Aberdeenshire to William the Waster, the lands of Roslin and others to Oliver, and the Earldom of Caithness to the second William. He died in 1480.
William the Waster received from his brother Oliver the lands of Ravenscraig, Dysart, and others. He had two sons: Henry, his successor, and William of Warsetter in Orkney. Henry was created Lord Sinclair of Ravenscraig in 1489.
John, seventh Lord Sinclair, died in 1676, and was succeeded in his estates by his daughter's son, Henry St.Clair, twenty-fourth Laird of Herdmanston, who was created Lord Sinclair in 1677.
Sir Oliver St.Clair, seventh Lord Roslin, was married three times, and had eight sons: George, William, Henry, Oliver, John, Alexander, Arthur and James. He died about 1520.
William St.Clair, fifteenth Baron of Roslin, sold his estates in 1736. He died without issue in 1778.
James St.Clair obtained a charter of Longformacus in Berwickshire about the year 1390. He seems to have belonged to the Roslin family. Robert Sinclair of Longformacus was created a baronet in 1664. Sir John Sinclair, the last of the Longformacus baronets, died in Edinburgh in poor circumstances, in 1798.
John Sinclair, a merchant in Edinburgh, purchased the lands of Stevenson in the counties of Edinburgh and Haddington in 1624, and was created a baronet in 1636. It is maintained that he belonged to the St.Clairs of Longformacus. Sir John Sinclair, fourth of Stevenson, had two sons: Robert, his successor, and George, Lord Woodhall. Sir Robert Sinclair, fifth of Stevenson, was succeeded by his son, Sir John, who obtained possession of the estate of Murkle in Caithness.