In this series as in many other works, Anderson presents vivid descriptions of natural scenes:
"Suddenly springtime billowed over the land. Warmth and lengthening days lured forth leaves. Grass glowed. The sky filled with wings and clamor. Lambs, calves, foals rollicked through meadows." (Time Patrol, p. 530)
But here he does more. This passage continues:
"Folk came from the gloom of houses, the smoke and stink of winter; they blinked in the brightness, breathed the sweetness, and set to work readying for summer." (ibid.)
(Lots of alliteration here.) The concluding sentence contrasts spring with winter in the minds of people living in first century Europe. This is the job of historical novelists, including historical sf novelists like Poul Anderson.