This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
The gate-posts and gates on every highway are a frequent source of interest to the lichen-ologist. They afford also to the student of flowering plants an easy means of wandering for a while from the highway on either side, and this makes the flora to be studied along a highway more varied and interesting.
About a gateway unusual plants will occur, such as Wart Cress, Charlock (Raphanus), Great Plantain, Knot Grass, various Cheno-podia, Docks, etc, dispersed from arable or similar open soil.
Pearlwort may be found on the sides of bridges, or Cerastium triviale, or Rumex Acetosella, and on a wet bridge over a road I have seen growing amongst the bricks, Epilobia, Scrophularia aquatica, etc. In the water or on the margin, aquatic plants may be found, such as Glyceria, Catabrosa, Lythrum, etc. Where heaps of stones have been thrown down and then cleared away, on the open ground one may find Red Poppy, Fumitory, Shepherd's Purse, Persicaria, Spurrey, Charlock, Wild Oat, etc, weeds that have strayed there from the cornfield or elsewhere quickly colonizing the new ground.
It is a common fallacy to suppose that the earliest roads were made by the Romans. But since there are a great number of other roads of importance, and certainly early origin, not made like those of the Romans, it is better to consider that these other roads are the earlier, and that the Romans took the roads they found and improved them themselves.
This is, moreover, shown by the occurrence along Roman roads of implements of the Bronze and Neolithic Ages, and Pre-Roman earthworks and burial-places with pottery, etc, as well as tumuli and other remains of Roman age.
The situation of some of the oldest sites of early civilization along the highway is in any case largely responsible for the introduction of plants into this country. Flax and some of the cereals were brought by the early peoples from the Continent, and the subsequent colonization of the country by Anglo-Saxons, Danes, Normans, and others has in each case augmented the original native flora, and it was largely by the agency of the ancient highways that these plants found their way into the districts where now they are considered to be native.
Owing to the effect of the Ice Age it was not possible in the Palaeolithic or early Stone Age for any direct tracks to be made across the country as in later times, nor was man then able to construct such roads, for his implements were of the crudest character, and his intelligence of no higher order. When the climate became ameliorated, man in the New Stone Age or Neolithic period was able to traverse the country more easily, and means of communication became a necessity as the beginnings of trade and agriculture became possible.
So it is found that there are certain types of ancient road which date from the ensuing era or Bronze Age. The low-lying country was then of a marshy and unsuitable character for cultivation, and impassable, so that the roads at first ran along the ridges, and are known as ridgeways. Remains found along these roads are the earliest. Next to these were hillside roads, which ran along the sides of the valleys or the hills dividing them. These were made in the late Bronze Age. Of a still later type are the harrow ways of the South of England, which are of late Celtic Age, just preceding the Roman period, and it is probable that these were largely utilized by the Romans in making their own way across the country. All these types are high-level roads, and the low-level roads were not made until the country was brought under cultivation and drainage after the felling of forests.
The distinction between these types of roads is important in estimating the relative age of introduction of plants by such means as roads.