[1] The occasional rockfall from the precipice above added boulders to the dune so the formation seen today is a consolidated composite of rocks and windblown sands.

The upper limits of the dune were scarped by the British garrison for two reasons - to avoid soldiers deserting the place and to prevent surprise attacks by Spanish troops.

Of late years, much labour has been bestowed in making all these parts more abrupt and difficult, yet it is still necessary to watch them, as there are always some hardy adventurers who will wantonly risk their lives down these perilous cliffs, either in attempting to desert or in search of flowers.

The catchment which was the original idea of the then City Engineer of Gibraltar and was constructed in 1903 on the Great Sand Dune which has an average inclination of 1⅓ to 1.

This dynamic nature meant that little vegetation of any significant height could grow on the dune with any permanence as many pre-catchment photographs demonstrate.

[1] In 2001, the Gibraltar Ornithological and Natural History Society began to manage the phased work of dismantling the catchment construction.