Why did the Roman army base on infantry?

[Domen]

Perhaps the most logical answer would be that infantry holds ground. The Roman army was aimed at expanding their sphere of dominance. Also important is that they had, certainly in the earlier centuries, an infantry based fighting style that worked very well against their unarmored and largely undiciplined opponents. The backbone of any army is the infantry, the grunts who slog it out, so too with the Romans. IMHO the ability of laying siege is not a dominant factor in the strategic choice for infantry, but it is certainly an added benefit.

But this alone surely does not yet fully explain the phenomenon. There were other empires in history - such as for example the Parthian-Sassanid Empire, the Mongol Empire (and other nomadic empires - but the Mongol Empire was the most long-lasting of them all) or the Han China Empire - which certainly also aimed at holding ground and expanding their spheres of dominance, but they relied either mostly - or at least to much greater extent than the Roman Empire - on cavalry.

I would rather agree with the explanation given by Mark Hygate.

The Han Empire was able to field enormous cavalry forces for their major campaigns. For example in 126 BC against Xiongnu they fielded over 100,000 cavalry, similar number was fielded in another campaign against Xiongnu in 119 BC - two cavalry armies 50,000 strong each (in total also 100,000 cavalry).

Apart from cavalry, they were also capable of mobilizing enormous numbers of chariots if needed. For example "The Military Storehouse of YongShi's 4th year Equipment Account Book", which lists equipment stored in Donghai Commandery, mentions 7174 chariots of 22 different types.

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The Han Empire developed an organized system of breeding good quality horses on almost industrial scale. I'm not sure if the Roman Empire was also breeding horses in state-owned stables and stud farms?

Such a quotation:

http://www.chinahistoryforum.com/index.p...topic=3082

2. Secondly, Han Wudi began to build up and improve the Han cavalry force. Through various means (involving smuggling and buying), he began to obtain better breed of horses from the XiongNu and Central Asia (known as the western region). Many stables were built across the empire to encourage these better breed horses to mate and some 100,000 better breed horses were built up. He also ordered that the cereal for these horses be improved.