Margary numbers are the numbering scheme developed by the historian Ivan Margary to catalogue known and suspected Roman roads in Britain in his 1955 work The Roman Roads of Britain.^[1] They remain the standard system used by archaeologists and historians to identify individual Roman roads within Britain.^[1] It is not known how the Romans identified the roads they built within Britain, and well-known names such as Watling Street and the Fosse Way largely date from the Anglo-Saxon period, are sometimes ambiguous or duplicated, and cover only a small proportion of the known network.^[2]

Margary's numbering system follows similar conventions to modern road numbering systems.^[1] He divided roads into three categories: Main Routes are given single-digit numbers, Principal Branches two-digit numbers and Minor Branches three digit numbers.^[3] Individual sections of longer routes are identified by adding letters to the route number, for example Dere Street (Margary 8) is divided into sections 8a, 8b, 8c, 8d and 8e.^[1] Double letters are sometimes used to indicate parallel or alternative routes.^[2] Lesser roads in particular areas are given similar numbers – for example many roads in Wales have numbers in the 60s.^[2]

Margary's cataloguing system has been criticised as being essentially arbitrary in several respects.^[4] Margary's hierarchy of routes is not necessarily that of the original designers or users of the network.^[5] Evidence for whether the Romans considered different lengths of road to form parts of a single route can be ambiguous, so the fact that they are given a single Margary number can be misleading.^[1] Margary's network also largely consists of roads built by the Romans, not necessarily roads used by the Romans, who may have continued to use native British trackways.^[6]

Margary's system is nonetheless widely used for its practicality,^[4] and the awarding of a Margary number to a route came to be considered a hallmark of authenticity among researchers in the field.^[7]