The autumnal biggy at the National Gallery, London, is Renaissance Siena: Art for a City, from 24 October 2007 to 13 January 2008. "Around one hundred beautiful paintings, sculptures, drawings, manuscripts and ceramics will be included in the exhibition." It will be in the Sainsbury Wing, admission £9. Silver surfers should go on Tuesday afternoons 2.30-6pm for a half price deal; otherwise you get belted £8. Francesco di Giorgio Martini is one of the artists whose work will be on display. I didn't think much of NG's example, so I found this jolly Madonna on the Internet. Francesco was better at designing military fortifications than he was at painting. It seems surprising to us how often Renaissance artists turned their hands to architecture and built castles for the local duke; but those were bloody times, and fortifications came before Art.