of those floors.) The top of the brick base was designed as an elevated courtyard melding the fourth floor of the city hall with the plaza. Security concerns caused city officials in recent years to block access to the courtyard and the outdoor stairways to Congress Street and the plaza. The courtyard is occasionally opened up for events (such as the celebration of the Boston Celtics championship in 1986). After the September 11 attacks in 2001, security was further increased. The north entrance, facing the plaza, was barricaded with jersey barriers and bicycle racks. All visitors entering the front and the back entrances must pass through metal detectors. City Hall was constructed by using mainly cast-in-place and precast Portland cement concrete and some masonry. About half of the concrete used in the building was precast (roughly 22,000 separate components), and the other half was poured-in-place concrete. All of the concrete in the structure, except that of the columns, is mixed with a light, coarse rock. While the majority of the building is created using concrete, precast and poured-in-place concrete are distinguishable by their different colors and textures. For example, cast-in-place elements are coarse and grainy textured because the concrete was poured into fir wood frames to mold it, and precast elements, such as trusses and supports, were set in steel molds to gain smooth, clean surfaces. This distinction also originates from the different types of cement used: the exterior poured-in-place pieces are of type I cement, a lightly colored cement, while the exterior precast components use type II cement, a dark-colored cement. The base of the building is dark with brick, Welsh quarry tiles, mahogany walls, and darker concrete. As the building ascends, the overall color lightens, as lighter concrete is used. Reception The public response to Boston City Hall continues to be sharply divided. Arguments for and against continued use of the structure provoke strong counter-arguments from politicians, local press, design professionals, and the general public. City Hall was given two stars by the Michelin Green Guide, which said that the building "has been one of Boston's controversial architectural statements since its completion in 1968." The building's 50th anniversary in 2019 prompted both positive and negative commentary. In the 2021 Boston mayoral election, candidates for mayor Andrea Campbell, John Barros, and Kim Janey voiced negative opinions on it, Annissa Essaibi George was neutral on it, while Michelle Wu voiced