On the nature of things (books 4 - 6)   

Of flesh and blood existing in the lands,
How could it be that she, Chimaera lone,
With triple body- fore, a lion she;
And aft, a dragon; and betwixt, a goat-
Might at the mouth from out the body belch
Infuriate flame? Wherefore, the man who feigns
Such beings could have been engendered
When earth was new and the young sky was fresh
(Basing his empty argument on new)
May babble with like reason many whims
Into our ears: he'll say, perhaps, that then
Rivers of gold through every landscape flowed,
That trees were wont with precious stones to flower,
Or that in those far aeons man was born
With such gigantic length and lift of limbs
As to be able, based upon his feet,
Deep oceans to bestride; or with his hands
To whirl the firmament around his head.
For though in earth were many seeds of things
In the old time when this telluric world
First poured the breeds of animals abroad,
Still that is nothing of a sign that then
Such hybrid creatures could have been begot
And limbs of all beasts heterogeneous
Have been together knit; because, indeed,
The divers kinds of grasses and the grains
And the delightsome trees- which even now
Spring up abounding from within the earth-
Can still ne'er be begotten with their stems
Begrafted into one; but each sole thing
Proceeds according to its proper wont
And all conserve their own distinctions based
In Nature's fixed decree.

ORIGINS AND SAVAGE PERIOD
OF MANKIND

But mortal man
Was then far hardier in the old champaign,
As well he should be, since a hardier earth
Had him begotten; builded too was he
Of bigger and more solid bones within,
And knit with stalwart sinews through the flesh,
Nor easily seized by either heat or cold,
Or alien food or any ail or irk.
And whilst so many lustrums of the sun
Rolled on across the sky, men led a life
After the roving habit of wild beasts.
Not then were sturdy guiders of curved ploughs,
And none knew then to work the fields with iron,
Or plant young shoots in holes of delved loam,
Or lop with hooked knives from off high trees
The boughs of yester-year. What sun and rains
To them had given, what earth of own accord
Created then, was boon enough to glad
Their simple hearts. Mid acorn-laden oaks
Would they refresh their bodies for the nonce;
And the wild berries of the arbute-tree,
Which now thou seest to ripen purple-red
In winter time, the old telluric soil
Would bear then more abundant and more big.
And many coarse foods, too, in long ago
The blooming freshness of the rank young world
Produced, enough for those poor wretches there.