The castle, of medieval origins, had been in ruins after a raid in the 1440s.
He enlarged and enriched it not only as a military base for his troops, but also as a seigneurial residence which should show off his success, in the typical Italian Renaissance fashion.
The castle is on a square plan, surrounded by two lines of walls and a ditch. The first line, now disappeared, included the stables and the barracks. The walls are characterized by merlons of medieval origins.
The castle's internal walls are almost entirely frescoed, although some of them have deteriorated or have been vandalized.
They celebrate the visit of King Christian I of Denmark in 1474 and the sumptuous hospitality given him by Bartolomeo Colleoni, including banquets, hunting expeditions and tournaments. They were commissioned by Bartolomeo's heirs around 1520-1530 to celebrate the family's most famous member, and are attributed to Il Romanino. On the first floor are 17th-century frescoes of lesser quality.
Aside from Christian I's visit, the frescoes depicts also allegories, such as that of the Silence (an allusion to the secret which should be kept by the castle's personnel), and the idealized portraits of Colleoni and the king. In the courtyard, also attributed to Romanino, is the depiction of the Battle of Molinella (or Riccardina), fought by Colleoni in 1467 near Bologna. Another 15th-century fresco of the Madonna with Child, from an unknown artist, is found in Colleoni's private studio.
- Cornazzano, Antonio (1990). G. Crevatin, ed. Vita di Bartolomeo Colleoni. Manziana: Vecchiarelli. ISBN 88-85316-16-6.
- G.I Guelfi e Ghibellini in Bergamo, Finazzi (1870). Bergamo. Missing or empty
- Page at icastelli.it (Italian)