Articulated locos are larger - they would have arrangements like 2-8-8-0 or 2-10-10-2. They are so long that they are essentially two locomotives tied together (to enable them to bend in the middle so they can take the curves)

The Henry Ford Museum in Dearborn has a C&O Allegheny 2-6-6-6. It's not the largest ever made, but it's the largest I've ever seen.