External staircases, Venice

I have noticed quite a few cantilever stone stairs around Venice. Typically the treads have a plain rectangular cross section with no rebates between treads, presumably this is for durability.

It would be interesting to know how far these treads are built into the walls and if any kind of mortar is used between each tread. I have seen flights in the UK that have been badly damaged where mortar between treads has been washed out leaving the treads wobbly in the wall.

Untitled (2012-10-25 15:57:55)