Carlo Fontana designed three projects for the Czech lands. All projects were either negotiated or directly commissioned by the Count Martinic who served as the Imperial ambassador in Rome. These projects included the rather utopian and non-realized project of the Liechtenstein Palace for Lanškroun, the project of the Šternberk/Sternberg Palace in Prague, which was not realized as well, and the project of Martinic/Martiniz Palace for the same town. I focus on the realized project of the Martinic Palace. Since the publication of the Windsor plans for all three projects, the Martinic Palace was given a repeated attention in modern scholarship. The up-to-date best description of the Fontana´s vision of the palace by Fiedler 2004 was, however, seriously weakened by the fact that its author did not take into account the project´s relationship to the Palazzo Grimani in Rome. The more precise understanding of the existing building was made difficult by the fact that the palace serves as the barracks of the President´s Guards and was not accessible before 1989. The results of its meticulous analysis have never been published and, as a manuscript, are available in Czech language only. I present a new interpretation of the building´s history base on a new direct research of the structure itself, the related archive documents and of a new reading of the geometric and proportional system incorporated in the preserved plans. The new reading of both the plans and the executed structure should help us to understand better the designing process balancing the ideal typology with demands defined by the character of the place and with an extremely delicate composition uniting the fronts and the ground plan of the palace in one indivisible whole base on subtle and precise geometry. This reading should also contribute to our knowledge of decision-making processes in the aristocratic milieu of the late 16th and early 18th centuries.