St. Martin's Le Grand was a former parish and liberty within the City of London, and is the name of a one-way street north of Newgate Street and Cheapside and south of Aldersgate Street.
To the east of the road once stood the collegiate church and monastic precinct of St Martin's, of ancient origin. The precinct was within the City, but was not subject to its jurisdiction, constituting a liberty with the privilege of sanctuary.
According to a somewhat dubious tradition, the church dated to the 7th or 8th century and was founded by King Wihtred of Kent. It was, more certainly, rebuilt or founded about 1056 by two brothers, Ingelric and Girard, during the reign of Edward the Confessor. Its foundation was confirmed by a charter of William the Conqueror, dating to 1068. The church was responsible for the sounding of the curfew bell in the evenings, which announced the closing of the City's gates. It was dissolved by King Henry VIII and demolished in 1548. It retained certain rights of sanctuary until 1697 and, as such, was a notorious haven for malefactors. One who sought sanctuary here was Miles Forrest, one of the reputed murderers of the Princes in the Tower.
The General Post Office established its headquarters on the site of the monastic precinct in 1829. From here mail coaches departed for destinations across the country. Coaches bound for the north went up St Martin's Le Grand through Aldersgate – the first section of the Great North Road (now the A1 route) to York and Edinburgh. It replaced the previous starting point at Hicks Hall in Smithfield Market. The Post Office building, a Neoclassical design by Robert Smirke, was demolished in 1911 and replaced by new premises immediately to the west, on the former site of Christ's Hospital school.