Brutalism, says Barnabas Calder, author of Raw Concrete: The Beauty of Brutalism, is hard to define, but easy to recognise. In this considered essay, he argues that whilst exposed concrete is now the key identifier for most of Brutalism’s fans, it is the structural potential of concrete that excited architects most at the time. However, Calder says understanding how it emerged from cheap energy sources in the mid 20th Century will help us adapt its example today.