A crucial issue connected with the actual conservation of old masonry elements is the compatibility of the new material applied to heritage structures. Knowledge of the physical, chemical and mineralogical properties of bricks represents a key point in this regard. In order to evaluate the fine internal structure of brick, an investigation of samples from three types of ceramic bricks has been carried out using both destructive and non-destructive techniques, such as X-ray powder diffraction, Fourier-transform infrared spectroscopy, Thermogravimetric analysis, and Scanning electron microscopy. An evaluation of internal damage and porosity distribution was also performed by means of micro-CT analyses. The bricks tested came from different historical periods: solid brick from the ruins of a medieval castle in the southern part of Poland ("hand-made" from the 14th century), solid clay brick from the turn of the 18th / 19th century and, for comparison, a new solid clay brick with a mean compressive strength not less than 15MPa. Our results show the variability of the main mineralogical and physical properties of the bricks from the reference periods analyzed, specifically the different ratios of quartz to feldspar and the decrease in mullite (Al6Si2O13) and iron oxides content from the oldest to the newest material reflecting the amount of clay in the green body. Compressive tests on non-standardized cubic samples were performed, showing the highest values for the material coming from the 18th century. Reasons for such a behavior are principally related to the reduced level of porosity and the pore morphology and size distribution.