The world's longest and heaviest train was incredible 4.5 miles long pulled by 8 engines

Freight trains transport billions of tonnes of cargo annually, including raw materials and finished goods. They have grown exponentially in size throughout the C20 and C21st, largely due to the high durability of the track network, modularity of the wagons, and the ability to use more than one locomotive to haul much larger weights.

Some of these giant serpentine trains consist of over 100 freight cars and several locomotives. In Brazil, freight trains operated by Carajás Railway and transported iron ore and pulp.

India's longest freight train is known as "Rudrastra" and is a whopping 4.5 kilometres in length. It consists of 354 wagons, powered by seven locomotives working in perfect coordination.

But it is in Australia that the world record for the longest and heaviest freight train has been set. The BHP Iron Ore Train is designed to transport huge volumes of iron ore from Western Australia's Yandi Mine to Port Hedland.

It takes about 10 hours for the train to cover its 275 kilometre route, which it first did on June 21, 2001.

The engineering marvel is 7.3 kilometres long (4.5 miles), making it almost the length of 22 Eiffel Towers lined up end-to-end.

It is made up of 682 wagons on 5,648 wheels and is pulled by eight locomotives, operated by just one driver.

The locomotives are spaced nearly a kilometre apart, but thanks to an ultra-modern distributed power control system they can be controlled by just one person.

The system allows all eight locomotives to accelerate, brake, and coordinate simultaneously, ensuring smooth movement despite the train's enormous mass.

Its record-breaking payload currently stands at 99,734 tonnes of iron ore, contributing to a total train weight of over 100,000 tonnes.

At the time of its launch, Mike Darby, BHP Iron Ore's Vice-President, said: "It was an opportunity to push the technology to the maximum."