These two streets, forming one continuous thoroughfare, are so intimately associated in their annals, that it is almost impossible to write the history of one of them without constant reference to the other.

Aldersgate Street derives its name from the old City gate which was the north-western outlet of the City, and St. Martin's-le-Grand (formerly Martin's Lane) from the collegiate establishment which occupied the site of the older or eastern portion of the Post Office. In the last century, that portion from the Barbican to the Bars was called "Pick-axe Street." Aldersgate is supposed to have been one of the four gates of Roman London, and was in the line of an ancient British trackway, improved by the Romans into a road called Watling Street, which came from Dover, crossed the Thames by a ferry, passed along where the modern Watling Street is, emerged from the City by Aldersgate, and went onwards towards Verulamium (St. Albans). As to the origin of the name there are various discrepant presumptions. Some assume that it was so called because it was one of the elder, or one of the four original gates; others that it obtained its name from a Saxon—one Aldrich, the builder or re-edifier of it; but the most probable assumption is that it was so denominated from the alder, or elder trees which grew in great profusion in that locality. The wall, after leaving Cripplegate, proceeded westward for a short distance, then turned at a sharp angle to the south, along the present Noble Street, until it came to near where the Castle and Falcon stands, where it again took a south-westerly direction, past St. Botolph's Church and the Greyfriars' Monastery. As represented by Aggas's map, there were four semicircular bastions in the Noble Street portion, looking westward, and two in the line from Noble Street to Greyfriars, besides the gate at the end of St. Martin's Lane, which is there represented as a heterogeneous mass of buildings, fortified, and with two posterns, the centre arch being hidden by a low building standing in front of it. A little to the north-west of Cripplegate stood a watch-tower called the Barbican, on the north side of the street bearing that name. It was erected by the Romans, and was garrisoned by a cohort of soldiers, who had a threefold duty to perform: first to keep an outlook for approaching enemies, secondly to watch for the outbreak of fire in the City, and thirdly to keep a beacon blazing on the top to serve as a guide for travellers by night over the northern fens and moors. Bridgewater House, which was destroyed by fire in 1698, is supposed to have been built on the site, and now Bridgewater Square. Some remains of the old Barbican were to be seen here in the last century.

Very little is known of the earlier history of Aldersgate. Stow says "This gate was antiently at divers times increased with buildings, namely on the south side, a great frame of timber was set up, containing many large rooms and lodgings; and on the east side was the addition of one large building of timber with one large floor, paved with stone or tile, and a well therein curbed with stone to a great depth, and rising into the said room two stories high from the ground."

In 1610, Thomas Hayes erected a conduit a little way to the north of the gate, which was supplied with water brought in pipes from the Thames.

It was usual to grant the rooms over the gates as residences for officials of the Corporation, those over Aldersgate being generally appropriated to the city crier. There is among the Corporation Records a deed of grant, in Latin, dated 49, Edw. 3, 1378, which, translated, runs thus: "Be it remembered that we, William Walworth, Mayor of London and the Assembly of Aldermen, with the assent of the Commonality of the City aforesaid, by reason of the good service by Ralph Strode, Common Countor (pleader or common serjeant) unto us done and hereafter to be done, have given and granted unto the said Ralph all the dwelling houses, together with the garden and all other appurtenances, situate over the gate of Aldrichesgate, to have and to hold the same as long as he, the said Ralph, shall remain in the said office of Countor, it being understood that the Chamberlain for the time being during the next year shall cause at his own expense all and singular the defaults in the said house to be repaired, etc." In the reign of Elizabeth it was occupied by the famous printer, John Day. Frequently, as was usual with city gates, Aldersgate presented to the view of passers-by a ghastly garnishing of the dismembered limbs of traitors. Thus Pepys writes, October 20th, 1660: "This afternoon, going through London and calling at Crowe's (Alderman Crowe) the upholsterer in Saint Bartholomew's, I saw the limbs of some of our new traytors set upon Aldersgate, which was a sad sight to see; and a bloody week this and the last have been, there being ten hanged, drawn, and quartered."

The gate gives the name to a City ward which was instituted in 1285, which is divided into two sections, each with four precincts. The first Alderman was William de Maiener; of the subsequent Aldermen, two have been baronets, Sir Samuel Garrard, Lord Mayor in 1709, whose ancestor, Sir William Garrard, was Lord Mayor in 1555, and whose great grandson, Sir John, was created baronet in 1621. Sir Samuel was the fourth in the baronetcy, and left issue two sons, both of whom succeeded, and both of whom died unmarried, the younger in 1767, when the baronetcy became extinct. The other was Sir John William Anderson, Lord Mayor in 1798, created baronet the same year, who died without issue in 1813, when the title expired. Three Aldermen also have been knighted, viz., Sir Peter Floyer, Sir Thos. Halifax, and Sir Peter Laurie. The Liberty of St. Martin's College was comprehended in the ward, but was exempt from its jurisdiction. Before the fire of 1666 there were six churches in the ward, those of St. John Zachary, St. Mary Staining, St. Olave, St. Leonard, St. Anne, and St. Botolph; of these the first five were consumed in the fire, and St. Anne's only rebuilt. St. Botolph escaped with a scorching. The most important religious establishment in the ward was the Collegiate Church of St. Martin's-le-Grand. Tradition says that it was founded in the time of the early British Christianity, by Wythered, King of Kent, in honour of Cadwallon, King of Britain. It was repaired and endowed circa 1056 by two brothers (Saxons), Ingelricus and Edward or Gerard, which was confirmed by William I., after the Conquest, by charter, wherein it is declared to be a Royal free chapel, with a collegiate establishment consisting of a dean and a fraternity of secular canons, with many privileges and immunities, including exemption from outward, civil, and ecclesiastical jurisdiction, and the right of sanctuary within the limits of the liberty.

Ingelricus was the first dean, and after him several distinguished men held the office, of whom William de Wykeham, the famous architect, Bishop of Winchester and builder of Windsor Castle, rebuilt considerable portions of the College; and James Stanley, brother of the Earl of Derby, who was instituted in 1493, and is supposed to have been the last.

The college with all its appurtenances was given by Henry VII., in 1502, to the Abbot and Convent of Westminster, for the performance of certain religious ceremonials; and on the suppression of the abbey, 34 Henry VIII., was transferred to the newly-created dean and chapter. It was suppressed finally in 1548, 2 Edward VI., and the same year, as Stow informs us, "the church was pulled down, and in the east part thereof a large wine tavern was builded, and withall down to the west and throughout the whole of the precinct of the college, many other houses were builded and highly priced, letten to strangers borne and others such as then claymed benefitte of privileges grannted to the canons serving God day and night (for so be the words of the charter of William the Conqueror) which may hardly be wrested to artificers, buyers and sellers, otherwise than as mentioned in the 21st of St. Matthew's Gospel."

The curfew bell was rung nightly, at eight o'clock, from the churchtower. Edward I. issued a proclamation that "in consequence of the many mischiefs, murders, robberies, and beating down persons by certain Hectors walking arm in arm, none should be so hardy as to be found wandering in the streets after the curfew had sounded at St. Martin's-le-Grand. The other churches where the curfew bell was rung in the City were St. Mary-le-Bow, St. Giles, Cripplegate, and Allhallows Barking. At the sound of the bell the great gates of Aldersgate were closed, but the wickets left open, which were also shut and fastened as soon as it ceased ringing, and were not opened again until the morning excepting by a special order from the Lord Mayor.

In digging the foundations for the Post Office in 1818, a range of Saxon or early Norman vaults were discovered, which had belonged to the college, the remains of a crypt of the time of Henry III., and a stone coffin.