Sicily started producing its own stamps in 1858 but stopped two years later when it became part of the newly founded Italian state. During this period, there were a number of wars and military struggles, so the post took a variety of routes - overland, by sea, over the mountains, along the coast etc.
Because of this, the covers were often covered in handstamps denoting the stops they had covered en route. And because there was no postal union, the letters which reached the border required another set of postage marks to proceed to other states of Italy such as Piedmont or Umbria.
The stamps themselves show the head of Ferdinando II. I am afraid my photo doesn't do them justice, but they are beautifully designed and great care was taken in choosing the colours.
One thing amused me. The cancellations were specifically designed so that they didn't obliterate the image of the king's head: this would have seemed disrespectful. (The Sicilians are very keen to avoid this kind of 'disgrazia')
So the cancellations are designed to only affect the edges of the stamps. Incidentally, in cases where the stamps were stuck on sideways or upside down, the post office had carefully rotated the stamp to ensure that the cancellation did not affect the portrait. Beautiful cancellations, beautiful stamps, fascinating history.
Incidentally, I happened to visit the display with a friend of mine - a retired Austrian judge who spends much of the year in Venice and collects stamps from Sicily. He bought a couple of covers like this about 20 years ago and tells me that he couldn't afford them now. I don't know what Francesco Lombardo does for a living, but he's accumulated an incredibly valuable collection.
see also - John Dupont and collecting stamps in Jail
Jack Shamash's book - George V's Obsession - A King and His Stamps