Every year since June 21, 1436, at noon a ray of light penetrates through a small hole in the dome of the Cathedral of Santa Maria del Fiore in Florence and falls on a bronze plate embedded in the floor. That was the idea of the builder of the cathedral, Filippo Brunelleschi. The great architect Quattrocento who placed this architectural wonder on shaky ground and crowned its grandiose dome, wittily took care of its inviolability. The test is simple yet genius: if a ray of sunshine hits the plate – it can live in peace for another year. If it misses, look for displacements in domes or foundations – and start repairing, until some disaster happened. “The enormous egg that Brunelleschi laid brings tears to an eye long used to the glitter of cupolas” – that’s what Joseph Brodsky has been saying for the sixth century, thanks to the foresight of the architect.