  The ideal Renaissance city is designed as a star-shaped fortress, where the
streets and squares are organized to speed the movement of people and soldiers.
Symmetry and accessibility represent the key features for the organization of
the urban space. The resulting city is hierarchized and does not always
guarantee an optimal degree of connectivity. Taking the baton from the work
done by space syntax in the definition of properties of spatial graph
representation, we introduce a method to compute urban graphs from the
Euclidean representation, the corresponding line graph and the contraction of
nodes with the same urban function. We analyze the urban graphs of five
historic cities: Vitry le Fran\c{c}ois, Avola, Neuf Brisach, Grammichele and
Palmanova and compare the analysis restults with the corresponding results from
space syntax. Analysis of the spectral gap and the relative asymmetry
distribution show a similar structure for these cities. The irregular or
reticular housing structure seems to ensure connectivity and accessibility more
than the regular grids. However connectivity is ensured by the most peripheral
streets, which in the space syntax representation play a marginal role.
