The Contribution of the applied petrography to understard the urban development of Ferrara (Italy)

The urban development of Medieval towns in the Mediterranean area were often controlled by the previous roman square plant. Ferrara represents a peculiar case as it was funded after the roman times over alluvial deposits after the northward deviation of the river Po. Recent archaeological digs carried out old buildings, paintings, potteries, glasses, crucibles, useful to reconstruct the architectonic/urbanistic evolution of Ferrara as well as to understand various technological processes. This in turn gives information on daily life of the local population in different historical epochs. Particularly important have been the diggings performed to set up a heating system based on deep geothermal fluids. These diggings exhumed old buildings containing several archaeological objects. These testify the real extension of the town (before the disastrous earthquake occurred in the 1570), the presence of old fortification walls and castles, and the style of life of the relative population. In this framework, the petro-archaeometric studies also illustrate the evolution of the technologies of the ceramic and glass production. In the southern part of Ferrara, close to the fortification walls, on the river there was a landfill collecting the waste material of the historic ceramic/glass laboratories. These materials progressively led to a morphological-high that was successively "colonized" and included in the new wall ring during the Renaissance. These activities were localized in the southern part of the town to take advantage of the presence of the river that provided an easy way to transport and commercialize the raw materials and the finished products. The petro-archaeometric study of different stratigraphic horizons within these waste materials (fragments of pottery, glass, crucibles, part of instrument) gives a chronological sequence describing variations in the used raw materials and variations in the working techniques. Similarly very important are the waste materials recovered within old cisterns found in the courtyard of various important buildings (i.e. Palazzo Schifanoia, Palazzo Paradiso, Monastero di Sant. Antonio in Polesine). In particular, the petrographic approach allowed to characterize production processes of potteries dedicated to the daily purposes (mainly used for cooking and to maintain foods), that considering the repetitively of the shapes and for to lack of the decorations, have not been studied in detail by previous studies. In fact, the petrographic study allowed to identify the areas of production of the ceramics, recognizing the starting raw materials as well as the firing temperatures. Comparisons have been made to understand the relations between the uses and the compositional and structural characters of ceramics (ceramics for water, for cooking, for the foods conservation, plates). The digs of via Ragno and via Porta Reno, reached the depth of 6 mt. showing that Ferrara in the upper Middle Ages was constructed mainly in wood as in many North-European sites. In via Porta Reno the dig recovered a remarkable collection of potteries, pots in ollare stone and decorative ceramics. We identified their character and the chronological evolution from the mineralogical and petrographic point of view. In the dig of Sant Antonio in Polesine cloister the recover of precious object highlight the high quality standard of life, also suggesting the presence of a pottery laboratory inside the monastery. The petrochemical analyses of glasses indicate that Ferrara in middle ages was an important area in the experimentation of glass production and that was competitive with the Venetian laboratories. Most of the recovered glasses are homogeneous in composition (prepared with a sodic flux), whereas glasses rich in potassium are rare and seem to be imported from elsewhere.