This is one of the cannon on display directly outside the Palace of Monaco. There are quite a selection of old cannon arranged around the square and all quite accessible. There is also quite a collection of cannon balls. There was no plaque on the cannon, but I'm reasonably sure it's a Model 1857 12-pounder Napoleon. From "Artillery compared and Contrasted" by Michael E. Haskew:"Named after Emperor Napoleon III of France, the Model 1857 12-pounder could fire a 5.6kg (12.3lb)projectile a distance of just over 1463m. Its bore was 117mm and its barrel length was 1670mm. The Napoleon was sometimes referred to as a "gun-howitzer" because it was considered by many to have characteristics of both."