Pienza , a town ( it : commune ) in the province of Siena , in the Val d'Orcia in Tuscany ( central Italy ) , between the towns of Montepulciano and Montalcino , is the `` touchstone of Renaissance urbanism . '' Pienza , a town and comune in the province of Siena , in the Val d'Orcia in Tuscany ( central Italy ) , between the towns of Montepulciano and Montalcino , is the `` touchstone of Renaissance urbanism . ''