A chemin de ronde — also called an allure or, more prosaically, a wall-walk — is a raised, protected walkway behind a castle battlement

Battlement

A battlement in defensive architecture, such as that of city walls or castles, comprises a parapet , in which portions have been cut out at intervals to allow the discharge of arrows or other missiles. These cut-out portions form crenels...

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In early fortifications, high castle walls were difficult to defend from the ground. The chemin de ronde was devised as a walkway allowing defenders to patrol the tops of ramparts, protected from the outside by the battlements or a parapet

Parapet

A parapet is a wall-like barrier at the edge of a roof, terrace, balcony or other structure. Where extending above a roof, it may simply be the portion of an exterior wall that continues above the line of the roof surface, or may be a continuation of a vertical feature beneath the roof such as a...

, placing them in an advantageous position for shooting or dropping.