Margary numbers

Margary's numbering system follows similar conventions to modern road numbering systems. He divided roads into three categories: Main Routes are given single-digit numbers, Principal Branches two-digit numbers and Minor Branches three digit numbers. 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. Double letters are sometimes used to indicate parallel or alternative routes. Lesser roads in particular areas are given similar numbers – for example many roads in Wales have numbers in the 60s.

Margary's cataloguing system has been criticised as being essentially arbitrary in several respects. Margary's hierarchy of routes is not necessarily that of the original designers or users of the network. 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. 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.

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

Main routes and principal branches