Evolution has resulted in adaptation in ways that are energy efficient, fault tolerant and having uses in diverse situations. We can learn from the forms, materials and processes found in nature. Using biomimetic animal morphology in robots will let them better handle natural environments. Herd behaviour, symbiotic cooperation, stochastic traversal, will let groups of machines perform tasks even in unpredictable surroundings.
The terraforming machines in Horizon are modeled after large vertebrates. This is partly as a homage to previous life on earth. Resource efficiency is not an issue since the whole system is completely automated with potential endless supply of energy and materials. Machines can do their work in an organic fashion, making them robust and adaptive and work well with the natural environment and plants, animals and the returning civilization.
The Tallneck acts as a communication hub, keeping contact with all the machines having antennas. It functions as a radio tower, gathering data from all the machines and sending out new instructions. It also keeps connection with neighbouring Tallnecks, cauldrons and other Zero Dawn facilities, as part of the global radio network.
The Recon class of machines gather information about the terraforming progress and helps the other machines navigate the terrain. The Watcher uses optical sensors while the Longleg uses sonar, suitable for scanning beyond and beneath solid objects.
The Transport class of machines brings resources back to the cauldron for the continued production of machines and facilities. The Bellowback is specialized for liquid cargo while the Shell-Walker is used for transporting stuff in containers.
The Acquisition class of machines does the work on the environment. The Scrapper and Glinthawk recycle metal from failing machines. The Grazer produce biofuel for the machines. The Rockbreaker mines minerals underground. Other machines has different roles in detoxification, resource gathering and making the soil suitable for plant life.
Some machines may even have been intended to assist the first generation of humans, like the Strider and the Plowhorn.