?si=WxyK2XAukThVTpa7 Con­struc­tion on the Tow­er of Pisa first began in the year 1173. By 1178, the archi­tects knew they had a prob­lem on their hands. Built on an unsteady foun­da­tion, the tow­er began to sink under its own weight and soon start­ed to lean. Medieval archi­tects tried to address the tilt. How­ev­er, it per­sist­ed and incre­men­tal­ly wors­ened over the next eight cen­turies. Then, in 1990, Ital­ian author­i­ties closed the tow­er to the pub­lic, fear­ing it might col­lapse. ...