Sentence:  Another form of <WSD>machicolation</WSD> known as slot (or slit) <WSD>machicolation</WSD> was formed by leaving an open slot above and before a gate. Box <WSD>machicolation</WSD>, which Kennedy refers to as ‘true <WSD>machicolation</WSD>', appears in Early Islamic fortifications. The direct source is clearly Islamic, although box <WSD>machicolation</WSD> is also present on pre-Islamic Syrian tower houses. 
Meaning of the word marked with <WSD> tags:  An opening between corbels that support a projecting parapet, or in the floor of a gallery or the roof of a portal, of a fortified building from which missiles can be shot or heated items dropped upon assailants attacking the base of the walls.