However, in the ancient world a variety of animals were sometimes of more combative use.
Nothing quite matches the stature and might of an elephant. They could trample people to death, impale them upon their tusks or fling them aside with their trunks. Counter-intuitively, elephants are also very quiet creatures. This is because they lack the hooves of horses and have soft feet.
Although Hannibal is famous for crossing the Alps with elephants few of them survived, and by the time of his march through the Arnus Marshes there was but one still living.
Pyrrhus actually made far greater use of the beasts earlier in the 3rd century BC. They were a great asset for him in his battles against Rome (he had a 2-1 winning record), but cost him the battle at Beneventum (which had previously been named Maleventum and was renamed by the Romans after their victory). The elephants at Beneventum ended up going berserk and stampeded over much of Pyrrhus’ army.
After the First Punic War, I think, the Carthaginians realised the potential for this, and in the Second their riders had a mallet and big nail to hammer into the beast’s skull if it went berserk.
Seleucus is less well-known than Pyrrhus or Hannibal but perhaps made the most important use of elephants in warfare. He entered into an alliance with Chandragupta, a leading light of India at the time, and received 400 elephants or so as a present. He used these at the Battle of Ipsus and they played an instrumental role in the victory of Seleucus and his ally kings against Antigonus Monopthalmus. Horses will not charge elephants, understandably, and the 400 were used as a screen to prevent the cavalry of Demetrius Poliorcetes (including a young man called Pyrrhus) from riding back to aid his father. The defeat of Antigonus dealt a death blow to any hope of a unified Macedonian world, and the remaining kingdoms of Macedon, Thrace, Seleucia and Egypt were gradually devoured by Rome and Parthia.
They have the rather obvious advantage of being pretty fast, and were used extensively throughout ancient warfare. Intriguingly, whilst Rome always had very good infantry its cavalry was almost always dire. Alexander, on the other hand, had the excellent Companions and many other skilled horsemen, and himself rode the splendid Bucephalus.
The Parthians had two types of cavalry, both of which were brilliant. Their first was a mounted archer, skilled enough to fire a shot backwards as they galloped away. This type slaughtered the Roman army at Carrhae, after which Crassus’ career rather nosedived. The second was the cataphract, which was essentially a heavily armoured man on a heavily armoured horse. They were very difficult to stop or kill, and the greatest problem they faced may have been the hot weather.
Hannibal had excellent cavalry. The best of these were the Numidians, who were natural horsemen and had very good discipline. A huge potential problem for cavalry is the getting carried away and chasing your enemy too far, which cost Antigonus and Demetrius at Ipsus. The Numidians would shower the enemy with darts, then retreat, then attack again and so on.
I have read that horses are afraid of camels (or camelry, if you prefer). However, I have never led a cavalry charge at a caravan of camels and cannot verify this one way or the other.
Yes, snakes. No, I’ve not been sniffing glue.
Unlike elephants or horses (or dogs) snakes are not a likely creature to use in warfare. However, Hannibal, being a genius, found a brilliant way to use them during his later and less well-known career fighting the Romans after the Second Punic War. When fighting Eumenes, an ally of Rome, in a naval battle he developed a cunning plan. He had snakes collected and placed in clay pots. During the battle the pots were hurled onto the enemy decks and the snakes emerged, much to the horror of the defending sailors.
Bears. Well, one bear
This does veer away from classical history by about two thousand years, but is so brilliant it must be shared.
In WWII some Polish soldiers had a bear fighting with them. Wojtek was an enlisted soldier, found as a cub, and had a rather distinguished war record. He discovered a quite probably terrified enemy spy in a shower block, enjoyed drinking and smoking, and could carry heavy (for his human comrades) munitions with ease. He also saw action at Monte Cassino.
Whilst I’m on a tangent, I rather like bears. They have a sense of smell better than dogs, can swim, climb trees, run very quickly, have great dexterity and strength and are very intelligent. I think Lord Byron had one at university (pet dogs were banned).