It was in this Tus­can town that Renais­sance town-plan­n­ing con­cepts were first put into prac­tice after Pope Pius II decid­ed, in 1459, to trans­form the look of his birth­place. He chose the archi­tect Bernar­do Rosselli­no, who applied the prin­ci­ples of his men­tor, Leon Bat­tista Alber­ti. This new vision of urban space was real­ized in the superb square known as Piaz­za Pio II and the build­ings around it: the Pic­colo­mi­ni Palace, the Bor­gia Palace and the cathe­dral with its pure Renais­sance exte­ri­or and an inte­ri­or in the late Goth­ic style of south Ger­man church­es.