Frankfurt this year has been bigger than ever, and a quick look back at the show six years ago proves just how significant (in most cases) concept cars are.The Bugatti Veyron and Ford Start concepts were both show-stoppers, while low-CO2 engines and small city cars were also more prevalent than ever before. Radical new design directions were seen on a number of stands, not least Jaguar's, which previewed the first vehicle produced under design boss Ian Callum. Similarities in appearance between the R-Coupe concept and the new XF clearly show the progression that the firm has made. Citroen previewed a truly bizarre concept named the C-Crosser. Though looks wouldn't suggest it, there is some connection to the production C-Crosser. Click on the gallery to see all the best cars from Frankfurt 2001.