The article publishes an as yet unknown fundamental report on the history of the Cistercian Monastery in Sedlec near Kutná Hora and its Gothic Convent Church of the Assumption of Our Lady and Saint John the Baptist. According to annals dating back to the mid-fifteenth century, namely folio 169v in codex Mk 108 of the Moravian Library in Brno, the foundation stone for the new Convent Basilica was laid in 1304 by the Bohemian King Wenceslas II. This record thus gives a precise date for the commencement of work to build this exceptional example of Gothic architecture and presents further proof of the close ties between Wenceslas II and the Cistercian order and Heidenreich, the abbot of Sedlec. and Jiří Doležel.