These are not simple decorations; They are called railway ballast and they play crucial roles. They are made of quartzites, basalts and granites measuring 3 to 6 centimeters, which, through friction, distribute the loads of the tracks and trains, preventing soil deformations and derailments. Furthermore, the ballast dissipates the train's vibrations and helps filter water, preventing flooding. So, these little stones are more fundamental than they seem.