See :
http://en.wikipedia.org/wiki/Machicolation
A machicolation is a floor opening between the supporting corbels of a battlement, through which stones, or other objects, could be dropped on attackers at the base of a defensive wall. The design was developed in the Middle Ages when the Norman crusaders returned. A machicolated battlement projects outwards from the supporting wall in order to facilitate this. A hoarding is a similar structure made of wood, usually temporarily constructed in the event of a siege. Advantages of machicolations over wooden hoardings include the greater strength of stone battlements, as well as the fireproof properties.





Illustration of machicolations in use
The word derives from the Old French word *machecol, mentioned in Medieval Latin as machecollum and ultimately from Old French macher 'crush', 'wound' and col 'neck'. Machicolate is only recorded in the 18th c. in English, but a verb machicollāre is attested in Anglo-Latin.[1] The Spanish word denoting this structure, matacán, is similarly composed from "matar canes" meaning roughly "killing dogs", the latter being a reference to infidels.[2] A variant of a machicolation, set in the ceiling of a passage, was colloquially known as a murder-hole.

Machicolations were more common in French castles than their English contemporaries, and when used in English castles they were usually restricted to the gateway, as in the 13th-century Conwy Castle.[3

La piombatoia (o caditoia) è una buca a forma di feritoia fatta negli sporti delle rocche, nei ballatoi delle antiche fortificazioni, nelle volte delle torri e, talvolta, anche in abitazioni private. La funzione delle piombatoie consentiva la tattica militare della difesa piombante, la quale consiste nel far cadere sul nemico assediante (oramai prossimo alle mura difensive), sia liquidi infiammabili o bollenti, sia materiali solidi come laterizi o pietre.
http://it.wikipedia.org/wiki/Piombatoia

--------------------------------------------------
Note added at 9 min (2012-03-13 13:16:14 GMT)
--------------------------------------------------

Machicolations

--------------------------------------------------
Note added at 18 min (2012-03-13 13:25:22 GMT)
--------------------------------------------------

In French = mâchicoulis