Originally imposing multistory masonry affairs, by the end of the conflict they had these prefab "Rice blockhouses", designed by one Major Rice, that were double-walled corrugated iron cylinders that could have local rubble poured between the two layers of sheet metal to provide bullet resistance. There was a gabled roof that could be sat atop it, and the whole thing would act as a sort of mini FOB for a squad of infantry. Space these things a thousand yards apart along a railway and no part of it is out of rifle-shot of two blockhouses.
Seems ghastly manpower-intensive, but securing rear areas from roving Boer commandos must have seemed like nailing jello to a wall.
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