The Description of Britain, also known by its Latin name De Situ Britanniae ("On the Situation of Britain"), was a literary forgery perpetrated by Charles Bertram on the historians of England. It purported to be a 15th-century manuscript by the English monk Richard of Westminster, including information from a lost contemporary account of Britain by a Roman general (dux), new details of the Roman roads in Britain in the style of the Antonine Itinerary, and "an antient [sic] map" as detailed as (but improved upon) the works of Ptolemy. Bertram disclosed the existence of the work through his correspondence with the antiquarian William Stukeley by 1748, provided him "a copy" which was made available in London by 1749, and published it in Latin in 1757. By this point, his Richard had become conflated with the historical Richard of Cirencester. The text was treated as a legitimate and major source of information on Roman Britain from the 1750s through the 19th century, when it was progressively debunked by John Hodgson, Karl Wex, B. B. Woodward, and John E. B. Mayor. Effects from the forgery can still be found in works on British history and it is generally credited with having named the Pennine Mountains.

Charles Bertram was an English expatriate living in Copenhagen who began a flattering correspondence with the antiquarian William Stukeley in 1747 and was vouched for by Hans Gram, the royal librarian to King Frederick V. After a few further letters, Bertram mentioned "a manuscript in a friend's hands of Richard of Westminster,... a history of Roman Brittain... and an antient map of the island annex'd." A "copy" of its script was shown to David Casley, the keeper of the Cotton Library, who "immediately" described it as around 400 years old. Stukeley thereafter always treated Bertram as reliable. He "press'd Mr Bertram to get the manuscript into his hands, if possible... as the greatest treasure we now can boast of in this kind of learning." Stukeley received the text piecemeal over a series of letters which he made available at the Royal Society's Arundel Library in London in 1749. He had received a drawing of Bertram's map by early 1750, which he also placed at the library.

Bertram described his text's author as "Richard, monk of Westminster" (Latin: Ricardus monachus Westmonasteriensis). There had been a monk named Richard at Westminster Abbey in the mid-15th century and this was the approximate date offered by Bertram to Stukeley. Stukeley preferred instead to identify Bertram's "Richard of Westminster" with Richard of Cirencester (Ricardus de Cirencestria), who had lived at Westminster in the late 14th century and was known to have journeyed to Rome and to have compiled another history known as the Historial Mirror. Bertram fully adopted the suggestion and published his account under the name Ricardus Corinensis, from the archaic Latin form of Cirencester's name.

It has since become clear that the text was the work of an 18th-century forger. Bertram claimed to have borrowed the text from a friend who admitted he had come by it as an act of theft from an English library. Its complete absence from other manuscript lists and the lack of any trace of it among Bertram's surviving papers in Copenhagen has generally led to the conclusion that Bertram himself was Pseudo-Richard.

Stukeley read his analysis of the work and its itineraries before the Society of Antiquaries and published his paper with its extracts in 1757. He was excited that the text provided "more than a hundred names of cities, roads, people, and the like: which till now were absolutely unknown to us" and found it written "with great judgment, perspicuity, and conciseness, as by one that was altogether master of his subject". His account of the itineraries included an engraving reorienting Bertram's map to place north at the top.

Later in 1757, at Stukeley's urging, Bertram published the full text in a volume alongside Gildas's Ruin of Britain and the History of the Britons traditionally ascribed to Nennius. The collection, in Latin, was titled Britannicarum gentium historiae antiquae scriptores tres (Three writers of ancient histories of the British nations). Bertram's preface noted that the work "contains many fragments of a better time, which would now in vain be sought for elsewhere". The preface goes on to note that, "considered by Dr. Stukeley... a jewel... worthy to be rescued from destruction", Bertram printed it "from respect for him". The volume included a map as well, differing from Stukeley's in several features apart from its orientation.

It contained 18 routes (Latin: itinera) of the type found in the Antonine Itinerary, compiled from fragmentary accounts of a Roman general, adding over 60 new and previously unknown stations to those mentioned in the legitimate account. Best of all, it filled up the entire map of Scotland with descriptions and the names of peoples, the part of Britain about which the least was known with any certainty. It would later be determined that it was actually a clever mosaic of information gleaned from the works of Caesar, Tacitus, William Camden, John Horsley, and others, enhanced with Bertram's own fictions.

Bertram's letters to Stukeley proposed that the map accompanying the text was even older than Pseudo-Richard's text. His letters state that he bought a copperplate to engrave it himself. Either this original copperplate or a freehand drawing was sent to Stukeley in late 1749 or early 1750 and formed the basis of the version reoriented and published by Stukeley in his 1757 Account.