'I found Rome a city of bricks and left it a city of marble,' Caesar Augustus apparently boasted. If so, he wasn’t the only person to dismiss the humble brick. They’ve housed us for tens of thousands of years. They are all rather similar – small enough to fit into a human hand, and half as wide as they are long – and they are absolutely everywhere. Why, asks Tim Harford, are bricks still such an important building technology, how has brickmaking changed over the years, and will we ever see a robot bricklayer?