This lovely old functioning theater, complete with impressive chandeliers, was where a tribunal met in 1867 to decide the fate of Emperor Maximilian. Mexico's constitution was also signed here on January 31, 1917. The stage backdrop lists the names of its signatories and the states they represented. In 1929 politicians met in the theater to organize Mexico's political party, the PNR (now called PRI). It's often possible to look inside.