[3] It remained the most prestigious residential address in the capital until the early 20th century when many of its former residents began to relocate to the city's newly developing suburbs.

In the last years of Austrian rule, plans were mooted to build a new residential district outside of the crowded city walls, in the area that would become the Leopold Quarter.

The area was designed to emanate from Brussels Park (located in front of the Royal Palace), and was laid out on a grid in a traditional classical pattern centred around the Square Frère Orban/Frère-Orbansquare.

[7] Other typical residents included civil servants, military officers, members of liberal professions, embassy staff, and representatives of foreign companies.

In those days, the outer edge of the area was bounded by the Maalbeek river valley, but in the 1850s, plans were drawn up to build a bridge across it to connect the Rue de la Loi/Wetstraat to the new military parade ground on the Linthout Plateau (today's Parc du Cinquantenaire/Jubelpark).

The City of Brussels bought the old zoological gardens and converted them into a public recreational park containing a variety of diversions, including the Museum of Natural Sciences.

In 1884, Ernest Solvay and Paul Héger, professors at the Université libre de Bruxelles (ULB), began a project to create an expanded university campus in the park.

Then after the Second World War, several insurance companies and colonial organisations began a trend toward demolishing the 19th century mansions and town houses, and replacing them with new modern office blocks.

Brussels had no development plan, and did not enforce existing legal restrictions, so most remaining residents left during this time as it had become completely transformed from a formerly quiet residential area into a congested centre of transport and business.