Merthin Fitzgerald is described in the novel as being of short stature and having bright red hair which he inherited from his ancestor, Jack Jackson - the main character from The Pillars of the Earth (2010).
Merthin, Ralph and their father Sir Gerald are descended from Jack and Aliena from Pillars of the Earth. Caris, her father Edmund Wooler, aunt Petronilla and cousin Brother Godwin are descended from Tom Builder through his daughter (and Jack's step-sister) Martha.
The Battle of Crecy (1346) as witnessed by Caris whilst in France was significant for two reasons. Firstly it heralded the rise of the longbow as the dominant weapon on the battlefield - a title it would keep until the 17th century and reliable handheld firearms. Secondly it was the first recorded use in battle of a cannon - called a ribauldequin and known as the "infernal machine". Having 12 barrels it was used by the English army, slow to load and liable to explode it nevertheless was the embryo of the gunpowder age
In the novel, Merthin and Ralph FitzGerald's father was not Earl of Shiring. Sir Gerald was an ambitious but impoverished minor nobleman. Sir Roland did not gain the Earldom at Sir Gerald's expense but was Earl from the start of the book.