Francesco di Giorgio

Francesco di Giorgio trained as a painter in Siena, in the workshop of Vecchietta, a leading local master, and yet Italy's rulers came to prize him for something else entirely, his skill at keeping armies out. He designed close to seventy fortresses for Federico da Montefeltro, the powerful Duke of Urbino, working out early star-shaped defences meant to deflect the new cannon fire of the 15th century.

He never stopped being an artist. He painted altarpieces, cast bronze reliefs and carved sculpture, and the serene painted panels of an ideal city that survive from his circle grew out of the same fascination with proportion and perspective.

For years he laboured on a great treatise on architecture and engineering, filling it with drawings of machines, water pumps, cranes and war engines. A copy ended up in the library of Leonardo da Vinci, who studied it and knew Francesco in person, the two of them consulting together in 1490 on how to finish the crossing tower of Milan's cathedral. He died in 1501, back near Siena, still better known in his own day for walls and machines than for the paintings that had first trained his eye.