11 Diagonal street is popularly known as one of the most idiosyncratic buildings in Johannesburg CBD. Constructed in 1983, it is a 22-storey high rise building with 2 floors below the ground in Diagonal Street, Johannesburg Central Business District. It stands 80metres tall and occupies a floor area of approximately 20,000m².

11 Diagonal Street was designed by an eminent architect named HELMUT JAHN. Helmut Jahn is a Chicago based, German-born American architect known for his postmodern steel-and-glass structures such as the said 11 diagonal street. His distinctive glass patterned designs began to make a mark in the late 1970s and 80s as they were seen to portray the central tenets of postmodern architecture like the Illusion Centre in Chicago, the  steel-and-glass arched roofs of the United Airlines Terminal at O’Hare International Airport, Two Liberty Place in Philadelphia, Munich Airport Center and much more modern 21st century structures such as the residential tower in New York and the said 11 diagonal street building also known as Diamond Building.

Diagonal street is one of the most iconic streets in Johannesburg. It is located in the western part of the CBD and is characterized by several historic architectural buildings and distinctive features. 11 Diagonal Street is fondly called Diamond Building as a result of its shape which has an angular facade similar to a multi-faceted diamond finished with glass curtains reflecting surrounding structures.

The architect, Jahn said, “The cut, reflective diamond became the selected Figure of Hope. The immediate vicinity of the building provided site suggestions for contextual relationships on which to develop a design.”  The shape of the building is directly inspired by the client’s identity and its design been constructed in the 80’s happens to be one of the best construction during the era.