The first man-made bridges with significant span were probably intentionally felled trees.

Such log bridges have a severely limited lifetime[3] due to soil contact and subsequent rot and wood-eating insect infestation.

Longer lasting log bridges may be constructed by using treated logs and/or by providing well drained footings[4] of stone or concrete combined with regular maintenance to prevent soil infiltration.

This care in construction can be seen in the French bridge illustrated below, which has well locked dry set stone abutments and a footpath leveled with boards.

Media related to Log bridges at Wikimedia Commons