The flat area south of the town can be divided into higher plain and lower plain. The higher plain stretches between the rivers Serio and Brembo, whereas the lower plain is split into two parts, Gera D’Adda (in direction of Milan) and Calciana (towards Brescia).

The via Francesca, a Roman road re-opened in the 9th century, splits the plain into two areas. The northern side is marked by morainic and permeable soil, small factories and fields planted with cereals.

The southern side is formed by a well-irrigated plain, impermeable soils that brought about the phenomenon of resurgence; extensive crops characterize large estates.

Today the plain includes several industrial areas like Treviglio and Dalmine, but the land is still dotted with castles and fortified farms. Worth mentioning are the castles of Brignano, Cavernago, Cologno al Serio, Malpaga, Marne, Martinengo, Pagazzano, Pumenengo, Romano di Lombardia, Solza, Torre Pallavicina, Urgnano.