There's no shortage of ways for an automaker to celebrate a big anniversary. Debuting a pivotal new product – like the new Giulietta – is one of 'em. Commissioning a series of concept cars – like the Pininfarina 2uettottanta, Bertone Pandion and Zagato TZ3 Corsa – is another. And so is hosting a huge rally for owners of its vehicles from around the world. Alfa Romeo, which this year celebrates its landmark centenary, is doing all of this and more.