This work address horizontal collisions between adjacent blocks, motivated by collisions between structures during earthquakes due to various mechanical properties, unsufficient gap between them and out-of-phase vibrations. The theoretical part deals with the description and analysis of pounding, presents practical examples and gives a historical overview of collision research. It also gives the equation of motion for rocking of a rectangular block on a rigid surface considering horizontal forces due to collision with adjacent blocks and describing the energy loss during collisions. The equations of motions are derived for three cases: translation of the block, rotation around point A, and rotation around point B of the block. Furthermore, two cases of energy loss that can occure during rocking blocks collide are explained: when blocks collide with the ground, or when blocks collide with each other. In the second part experiments are carried out, stability graphs are obtained and results from optical measurements are presented. Experimental part is carried out using the quanser STI-III seismic platform and GOM mbH PONTOS 3D 4M optical measuring system, while two types of samples, B6M and B8S, are used. The samples are placed on a seismic platform in three configurations, and the system is run by assigning various amplitudes and frequencies, while the response of the blocks is observed. The blocks either remain stable, overturn or rock periodically. From these tests, stability graphs are obtained. The optical measuring system monitored four selected experiments from which we obtained diagrams showing the displacement of the seismic table in time, the angles of rotation of the blocks and the distance between them.