the "invicta" was the twentieth robert stephenson & co. locomotive, and was built for the canterbury and whitstable railway. its cylinders were inclined, but moved to the front end. in 1830 came the "planet" class with the cylinders inside the frames, followed by the "patentee", which added a pair of trailing wheels for greater stability with a larger boiler. this 2-2-2 design became the pattern for most locomotives, by a variety of manufacturers, for many years.