Blockhouse

The blockhouses Charles' refers to looked like this one. They were built all over South Africa as a systematic way of trying to disrupt the Boer Commandoes. They made extensive use of barbed wire to fence off areas guarded by these blockhouses to ensure that the Boers couldn't move around the veldt with impunity.

Above Image courtesy of Imperial War Museum

They could be built in a variety of styles as the photograph below illustrates but all tended to have a small section of 10 soldiers commanded by an NCO.