Existence bookcase

Why must bookcases always be straight, long, vertical and with their shelves orthogonal to put books on straight and composed? Existence is a round metal bookcase that comes about from the overlapping of many modules that are similar, but never equal to each other in terms of dimensions, height and arrangement. Open spaces are created between the modules – inspired by the alleys between old houses in Italian villages – where little monuments can be placed: books organised by author, size, rejection or liking; small objects that are useful and useless, but fundamental for our existence.