I strongly strongly recommend the book The Bear: History of a Fallen King by Michel Pastoureau. For most of European history, the bear was the king of the animals, it was only as--and I know this sounds insane--that the bear fell afoul of Christian doctrine that it was eventually surpassed by the lion. Due to a misreading of Pliny, who claimed that bears copulated missionary style, medieval scholars believed that bears were sinful creatures.

Here is a solid review to start and a quote from it:

Like many primitive religious beliefs, these persisted well into the Christian era, surviving side by side with the orthodoxies of the Christian church. Hence came the abiding hatred of the medieval church for bears. St. Augustine of Hippo knew little or nothing about them. But he had read his Pliny and, building on the fables of the great Roman naturalist, bequeathed to the medieval centuries the standard Christian image of the bear: malicious, lewd, destructive, predatory. Ursus diabolus est: "The bear is Satan," he wrote. Saints and hermits were frequently described as taming bears, and reducing them to menial servants, in order to show the faithful how the power of God could exorcise the Devil and reduce him to harmless submission.

http://www.wsj.com/articles/SB10001424052970204524604576609443454965846

hi! check out this recent post for some more info, including links to other posts and the FAQ

• Were there actual lions in medieval Europe?

I think you have to bear in mind the symbolic associations of the lion, as well. The "Encyclopaedia of Traditional Symbols". (J.C. Cooper, Thames and Hudson, 1978) says: "As solar it represents the heat of the sun, the splendour and power of the noonday sun; the fiery principle; majesty; strength; courage; fortitude; justice; law; military might; the King of the Beasts; but it is also cruelty; ferocity; and the sub-human modes of life; it is a symbol of war and an attribute of war gods" and much else besides.

My family coat of arms has a lion rampant on it, and this family is from the north of Ireland. But this heraldic or symbolic lion might have very little to do with actual lions. People in the Middle Ages don't need to have seen an actual lion in order to conceptualise this heraldic lion, any more than they needed to have seen a real-life unicorn or dragon to conceptualise the heraldic unicorn or dragon.