As part of a historical building investigation of Schloss Tirol, the ancestral castle of the Dukes of Tyrol (South Tyrol/Italy), a mineralogical investigation of the two marble portals dated to the 12th century has been realised. An ultrasonic study of the square stones of the palace and the chapel portals has been conducted in order to characterise the marble in terms of ultrasonic velocities and to establish criteria for a possible different provenance of the building materials for both portals. The average ultrasonic velocity (UV) of the chapel portal square stones is 5 500 m/s which is significantly higher than that of the palace portal building stones with 4 000 m/s. This difference indicates a different provenance of the buildings stones and/or a different weathering history. Based on the ultrasonic data, a total of 23 square stones from both portals were cored in order to provide material for grain size, chemical and isotopic (16O/18O, 12C/13C) analyses. ?18O values for the chapel portal stones are very uniform with an average of -5.1±0.09(n=13). In contrast, values for the palace portal show a much wider scatter with an average of -7.6±2.2(n=10). Likewise, the Mn concentration in marbles from both portals is significantly different with 31±4 and 139±96 ppm for the chapel and palace portal stones respectively. A comparison with data obtained from marbles of nearby quarries suggests that the chapel portal was built using marble from Sterzing only whereas the palace portal was built using a variety of marbles presumably from Sterzing and Laas. The lower ultrasonic velocity of the palace portal stones would be consistent with a period of 100-200 years of unsheltered exposure in medieval times as suggested by certain architectural features.