Origins of the clan 
Since the eighteenth century, Barclay historians, noted for their low level in medieval scholarship, have assumed the Scottish family Barclay (de Berchelai) is a branch of one of the Anglo-Norman Berkeley family of Berkeley, Gloucestershire in Gloucestershire. However, the link between the Scottish and English families is disputed. The Collins Scottish Clan Encyclopedia agrees that the Barclays came over from France during the Norman conquest and that they settled in Gloucestershire, England where as the Earls of Berkeley, they built Berkeley Castle in 1153. Some of the family moved north to Scotland where they settled in Aberdeenshire and Fife.
An old family tradition is that the Scottish family is descended from John de Berkeley, who was the son of Roger de Berkeley, provost of Berkeley, and went to Scotland in 1069 with St Margaret. Another theory is that the clan is descended from a John de Berkeley who went north in 1124 with Maud, queen of David I.
Another theory of the Barclay origin, put forth by the historian G. W. S. Barrow, points to the small village of Berkley in Somerset (in 1086 Berchelei). In 1086 the overlordship of Berkley belonged to Robert Arundel, whose main tenant was a Robert. Arundel's manors included Cary Fitzpaine (in Charlton Mackerell), near Castle Cary. Cary Fitzpaine seems to have been held by the tenant Robert as well. At the same time as Henry Lovel of Castle Cary first appears in Scotland, there appear the names of Godfrey de Arundel and Robert and Walter de Berkeley.
The Barclays soon established themselves in strong positions in land offices and alliances, and took part in the Wars of Scottish Independence. In 1165 Sir Walter de Berkeley was Chamberlain of Scotland. Sir David Barclay was a close associate of king Robert the Bruce and was present at most of his battles, most notably the Battle of Methven where he was captured.
The main line of the Scottish Barclays has been represented by the Barclays of Mathers. The descendants of this line were noted in more modern times for producing field marshals, Quakers and bankers. Barrow also noted that Barclay historians fail to mention that this line had not been a Barclay in the male descent since the end of the twelfth century. Charters from the reign of William the Lion show that the king granted the Barclay estates of Laurencekirk and Fordoun to Humphrey son of Theobald, in right of his wife Agatha. Agatha, herself was a 'de Berkley' and her husband and children adopted her surname. A charter preserves Humphrey's father's surname as 'de Adevil(l)e'.
17th century 
In the seventeenth century one branch of the Clan Barclay established themselves at Urie, near Stonehaven in Kincardineshire. Colonel David Barclay, the first Laird of Urie was a professional soldier who fought for Gustavus Adolphus of Sweden. David Barclay attained the rank of major and returned to Scotland when the civil war broke out. During the civil war in Scotland he commanded a regiment of horse fighting for the king. He retired in 1647 but after the Restoration (1660) he was imprisoned in Edinburgh Castle on a charge of hostility to the government but was later released. While in prison he was converted into a Quaker by the Laird of Swinton who was also a prisoner. His son, Robert Barclay, was also a Quaker and published An Apology for the true Christian Divinity as the same is held forth and preached by the people called in scorn Quakers in 1675. Robert Barclay's second son, David Barclay, founded Barclays Bank.
Another branch of the Clan Barclay, the Barons of Towie were involved in shipping trade in the 17th century between Scotland and Scandanavia, and the lands around the Baltic. In 1621 Sir Patrick Barclay, the seventeenth Baron of Towie signed a letter of safe conduct for John and Peter Barclay, both merchants in the town of Banff, Aberdeenshire becaused they wished to settle in Rostock in Livonia.
Napoleonic wars 
Five generations after Peter Barclay was descended the Russian Field Marshal Michael Andreas Barclay de Tolly who was born in 1761. He was made Minister of War in 1810 and two years later was given command of the Russian armies who were fighting against Napoleon. The appointment of a Scottish commander-in-chief was resented by the nobles of Russia, however his capabilities were respected. He was created a prince by the Tsar and his memory is still honored in Russia where his portrait hangs in the Hermitage Museum in Saint Petersburg. He died in 1818.
Clan castles 
- Peter Charles Barclay of Towie Barclay and of that Ilk, Chief of the Name and Arms of Barclay and Representer of the House of Towie Barclay.
- Dress Barclay Tartan: (yellow and black with white overcheck).
- Ancient Hunting Tartan: (blue and green with red overcheck).
- Clan Barclay History Retrieved on July 28, 2007.
- Clan Barclay Geneaology Retrieved on July 27, 2007.
- The Kingdom of the Scots, p.331-334.
- Way, George and Squire, Romily. Collins Scottish Clan & Family Encyclopedia. (Foreword by The Rt Hon. The Earl of Elgin KT, Convenor, The Standing Council of Scottish Chiefs). Published in 1994. Pages 72 - 73.
- Clan Barclay: official site
- The Misty Origins of the Barclays baronage.co.uk. Retrieved 03 May, 2013.
- burkes-peerage.net BARCLAY