It's all about Power, baby!
The steam engine was arguably the most important technology of the Industrial Revolution.
As more goods were produced, more transport was needed to move them around. The canal system, which had been spreading since the mid-eighteenth century, was not sufficient, and road transport was slow, unreliable and costly. Railways filled this gap, helped by the development of new methods of producing iron and steel for construction, and more efficient steam locomotives.
Following the need of more and more power to fulfil the needs of an expanding industrialization, and the consequent urge to rapidly connect vast areas of the world, in the years between 1850 and 1950 the biggest steam locomotives were built, up to the 'Big Boy', able to pull a 3600 ton train at 130 km/h.
Even having precise needs and goals, the aesthetics of power had never been underestimated by the engineers of those times; it is clearly visible in any detail of their creations.
Those machines had to convey the feelings of strength and beauty together, using even the actual mechanical parts of the engine.
They are an astounding mixture of engineering, mechanics, design, and love.
[Oh, if you are curious about the guy in the photo, google for Isambard Kingdom Brunel...]