One of the windows looked out over the green fields of England: the other looked back into Wales...Culturally the central characters are Welshmen, with the surname Jones.
The story is told through the technique of flashback, and portrays the lives of twin brothers, Lewis and Benjamin Jones, on their isolated upland farm called The Vision. The twins develop a bond that is shown throughout the novel as very special. Lewis is portrayed as the stronger more masculine or dominant twin, whereas Benjamin is the more feminine or intuitive one, both in appearance and in the tasks which he does around the house. He seems to be constantly drawn to his mother's side while she is alive, and there is also a suggestion of more than a brotherly love toward his twin Lewis.
Lewis is the one who wants to break free but Benjamin joins the army at the time of the Great War but his efforts are frustrated by his family ties and the indefinable, unbreakable tie to the land. Chatwin also tells the reader of the brutality involved in farming at the time in this area. Amos, the father of the two twins, shows how his day-to-day job has brutalised his once caring and loving attitude, and we see this later in the novel when he hits his wife Mary on the temple with the book she is reading - Wuthering Heights. A jealous man attacks his wife with the very material that shows her intelligence; he feels threatened by this, feeling that the man is supposed to be the head of the family in all things, and he feels anger because of his limited education.
On the Black Hill is a novel which portrays themes such as unrequited love, sexual repression and confusion, social, religious and cultural repression, hate and the historic social values of that era, as is shown when Amos finds out that his daughter Rebecca has become pregnant by an Irishman. His religious fanaticism, social pressure, economic forces and an inability to express love results in him throwing her out of the household, and she is not mentioned in the novel again until the latter part.
The location is lightly fictionalised. Many real place names are used, the great majority indicating a site on the border of Herefordshire and Breconshire south of Hay on Wye. The Black Hill and Cefn Hill are outliers of the Black Mountains; Radnorshire lies just across the Wye to the north. Hay (with its castle and pre-war railway station) would be the principal town in the area but its name is notable by its absence; instead, is seems the name of the Radnorshire hamlet of Rhulen has been used. The name of the Shropshire location of Lurkenhope has been used for the principal village. On the Ordnance Survey map, 'Abergavenny and the Black Mountains, Wales sheet 161' (1:50,000 series) and even better depicted on the more detailed 1:25,000 series at the Black Hill itself is shown, towards Craswall. The name refers to a well known ridge descending very steeply from the very long Hatterall Hill ridge (which forms the England / Wales border) and carries Offas Dyke footpath on it, down into the fields of Herefordshire, and on the English side. The Black Hill is known locally as 'The Cat's Back' as viewed from Herefordshire it looks like a crouching cat about to pounce. On the same map at , just a little to the south, you will be able to see a real farm called The Vision Farm, situated in the Llanthony valley, also known as the Vale of Ewyas, on the Welsh side of the border, just below Capel-y-ffin.
Chatwin amalgamated reality with his research amongst the local indigenous populace in the time he researched the book, interweaving fact and fiction, gossip, locations, stories and social history.