In the 19th century, the second walls were torn down and replaced with the Small Ring, a series of boulevards bounding the historical city centre.

Construction of the first walls of Brussels is estimated to have taken place at the beginning of the 13th century, during the reign of Henry I, the first duke of Brabant.

They extended to the heights in the east of the city, enclosing the first Cathedral of St. Michael and St. Gudula (then a collegiate church) on the Treurenberg hill (French: Mont des pleurs; "Mount of tears"), where the St. Gudula Gate stood (integrated in these first walls), and which was later used as a notorious prison, hence its name,[2] as well as the ducal palace of Coudenberg.

Louis invaded Brabant and quickly seized Brussels, planting the Flemish lion flag in the middle of the Grand-Place.

This enabled Joanna and Wenceslaus to make their Joyous Entry into Brussels, granting a charter of liberties that would be seen as the equivalent of the Magna Carta for the Low Countries.

The design was fairly typical of medieval defences before the introduction of gunpowder, and was surrounded by a moat in the lower parts of the city.

The Fort of Monterey [nl; fr] was the most important defensive work, its name coming from the Spanish count responsible for modernising the defences.

The fort was built between 1672 and 1675, by the military engineers Merex and Blom, on the heights of Obbrussel (Old Dutch: Obbrusselsche, for "Upper Brussels", now Saint-Gilles), south of the Halle Gate.

[5] As with the rest of the city's fortifications, the fort was ineffective, and was not able to prevent the French bombardment of Brussels in 1695, from the heights of Scheut, in Anderlecht, as part of the War of the Grand Alliance.

[5] In 1795, when Republican France invaded and annexed the Low Countries, the demolitions were stopped, not resuming until an order from Napoleon in 1804.

With the return of stability, in 1818, authorities organised a contest for plans to demolish the ramparts and replace them with boulevards suited to the exigencies of contemporary life in the city.

A barrier with a ditch running its length was still installed, however, and toll pavilions built at the entrances, to allow continued taxation of commercial goods entering the city.

From 1868 to 1871, as the city was being modernised, the architect Henri Beyaert, with little regard for historical accuracy, transformed the austere medieval tower into something of a neo-Gothic castle, which fit better with the contemporary romantic perception of the Middle Ages.

Their course can be seen by the current Small Ring, although it stops short of the Halle Gate, and they still define downtown Brussels, often called the Pentagon.

In the 1950s, with pressure from the automobile, new plans to improve traffic flow were implemented, partly due to the 1958 Brussels World's Fair (Expo 58).