Well done to Earle A Bowen and GMG for getting the answer to yesterday's quiz. The invention in question is the dolos (pronounced almost like "door-laws" but with very short vowel sounds); these huge concrete blocks, shaped like the letter "H" with one arm rotated by 90 degrees, are used to protect beaches and breakwaters all around the world today. They were invented by one of two men (there is some dispute as to which one) in East London, South Africa in the 1960s. The name is derived from the Afrikaans word for an animal's knuckle-bone, to which these concrete blocks bear some resemblance.

Today's picture shows a large section of the breakwater in Table Bay Harbour, protected by thousands of dolosse.

Earle & GMG: please email your postal addresses to info@redballoon.co.za, so that I can send off your postcards.