This year marks the 50th anniversary of a design competition in which architects were invited to imagine a new Boston City Hall.

Architects Michael McKinnell (standing) and Gerhard Kallmann, photographed recently in Cambridge, won the design competition.

The city decided to demolish the neighborhood known as Scollay Square (pictured in 1906) and build in its place what would come to be called Government Center.

From the competition, Kallmann's drawing showing a cross section of the building.

A preliminary sketch from McKinnell shows the structural and mechanical systems of the building.

In the competition, architects were invited to imagine a forward-looking home for Boston's city government. Shown here, a design by Gertrude Kerbis, Yau Chun Wong, T. C. Chang, Otto G. Stark, Sam Sit, and C. F. Murphy Associates. This design made it to the second round of the competition, but did not win.

An overhead view of the previous design that made the second round of the competition, but did not win.

Another finalist from the competition, this one from Progressive Design Associates. The city announced the competition, which was uncommon in its time, in 1961.

This design by architects Ehrman B. Mitchell Jr., Romaldo Giurgola, and Thomas R. Vreeland was also a finalist. Eight finalists were chosen from among more than 250 submissions.

Kallmann and McKinnell’s winning design was selected in 1962.

Ground-breaking for the construction of the new City Hall building took place in September, 1963.

A look at Boston City Hall under construction in 1967.

City Hall, with its wide plaza, in 1998.