The 'Descriptio Urbis Romae' by Leon Battista Alberti: historical analysis, experimental hypotheses

The ‘Descriptio Urbis Romae’ by Leon Battista Alberti (1404-1472) is a work of great importance in the history of urban survey and representation and offers a precious starting point for reflection on the role of illustration in scientific texts. In the ‘Descriptio’ Alberti provides an easy method, elegant and suitable for anyone to represent the map of Rome, discretized in a finite number of points that correspond to natural (river, Tiberina Is-land) and artificial elements (walls, gates, important monuments). These points are described by a pair of polar coordinates that allow, thanks to an instrument described and illustrated in the text, to reconstruct the position of these points on the drawing. The drawing of Rome evoked by Alberti is very different from those typical of the previous and subsequent period, which gave a subjective view of the city trough bird’s-eye perspectives: it gives a discretized, abstract image of the city, measured and measurable. Among the others, there’s a surprising feature that make it so interesting: its absence. Not an unin-tentional lack, but a deliberate absence, which mainly depends on two interrelated factors: the hu-manist primacy of word over image in the Renaissance, the ‘age of eloquence’, and the difficulty to hand down accurately images by copyists in the manuscript tradition. While in China the xylography (VIII century A.D.) and the movable type printing (Bi Sheng, XI sec. A.D.) were already known and practiced for centuries, in Europe they began to spread only in the second half of the fifteenth century. Until then, the literati - including Alberti - preferred to entrust to ekphrasis - an extremely detailed text description - the transmission of drawings which they re-ferred, arguing that written text is less susceptible to errors than graphic one in the manuscript transmission. Unlike the Eastern tradition, which recognized in image an informative content nobler than that explained by words (Zhan Ruoshui, ‘Linghai Yutu’), Alberti considered illustrations, ex-pecially the medioeval ones, a vulgar communication tool. The Descriptio is actually the result of a far more complex process - partially revealed in its theo-retical essence by the same author in the ‘Ludi rerum mathematicarum’ - that aims at representation of the city through a direct survey of the elements that characterize it. This process, at the basis of modern urban survey theory, is the main subject of our study, which, moving by the observation by Luigi Vagnetti (1968), Mario Carpo and Francesco Furlan (2005) and with the support of the current digital technologies, intends to investigate the issues of survey re-lated to the technology and to the method used by Alberti. Through an experimental model, which takes into account such factors as the choice of the station points for the measurements, the accuracy of survey instruments and their orientation, we were able to verify the nature and extent of the deformation found in the map described by the author with respect to the real shape of the city of Rome.