The first mention of the Barony of Keith dates from 1160, when Sir Simon Fraser, the first Baron of Keith, donates a church to the Monks of Kelso:
...donacionem quam Symon Fraser eis fecit de ecclesia de Keth cum tota illa terra et toto nemore ab australi parte riuuli qui currit iuxta predictam ecclesiam..."
- Kelso Abbey Cartulary AD 1160, National Library of Scotland
This marks the start of recorded history for Clan Fraser in Scotland and thus also for Clan Fraser of Lovat, a Highland clan that emerged from Clan Fraser.
Edinburgh itself, the present-day capital of Scotland, evolved from a Celtic fortress called Din-Eidyn to a city (or Burgh, hence the name Edin-burgh). A city of such importance necessitated the protection of strong knights; hence, King David I had invited Norman knights such as Sir Simon Fraser and Hervey Fitz Warin, see below, to defend the southeast approach route to Edinburgh from invading southern armies.
The Barony dates from AD 1150, when King David I of Rìoghachd na h-Alba (or simply Alba, modern-day Scotland) donated land in East Lothian near Edinburgh to the Norman knight Sir Simon Fraser, who had helped defend the Kingdom of Alba that would become Scotland, as well as the city of Edinburgh. David I of Alba was canonized in 1175 by Pope Alexander III and is the patron saint of Scotland.
Around the same time, Hervey Fitz-Warin, also a Norman knight, gains adjacent lands in Keith through marriage of a local princess of the Pictish Cattra tribe. Then, Hervey's son marries Simon Fraser's granddaughter and heiress, Eda, thus consolidating the lands of Keith under one barony.
The Keiths and the Frasers, now united through marriage, would help shape much of Scotland's history in the centuries that followed.
The name Keith derives from the Celtic word for "wood" or "woodlands," which was an apt name for the forests that existed east of Edinburgh in the 12th century.
Clan Keith derives its very name from the Barony of Keith in East Lothian.
As the Keiths became Marischals and later Great Marischals of Scotland, the name Marischal was added to the barony, which became known as Keith Marischal.