The basilica st. Jiri on Prague Castle has two towers and three bodies. The north tower is deflected from vertical about 450mm. During the last measurement it was found, that the walls were diverted too. The reasons and beginning of fault genesis have not been known yet. It can be larger self weight of tower then weight of navy. It leads to different settlements during homogenous foundation conditions. The next reasons are not clear. I investigated: tower weakening by the door opening, influence of inside vault over middle navy, foundation conditions. The results obtained from numerical model show that every mentioned reason contributed to the deflection of the tower.