About 50 miles west of Stonehenge, buried in the peat bogs of the Somerset flatlands in south-western England, lies the oldest road known to humanity. Dubbed the “Sweet Track” after its discoverer, Raymond Sweet, this painstakingly constructed 1,800-meter road dates back to the early Neolithic period, some 6,000 years ago. Thanks primarily to the overlying layer of acidic peat, which has kept the wood moist, inhibited the growth of decay bacteria, and discouraged the curiosity of animal life, the road is remarkably well preserved. Examination of its remains has provided extensive information about the people who constructed it. The design of the Sweet Track indicates that its builders possessed extraordinary engineering skills. In constructing the road, they first hammered pegs into the soil in the form of upright X's. Single rails were slid beneath the pegs, so that the rails rested firmly on the soft surface of the bog. Then planks were placed in the V-shaped space formed by the upper arms of the pegs. This method of construction―allowing the underlying rail to distribute the weight of the plank above and thereby prevent the pegs from sinking into the marsh―is remarkably sophisticated, testifying to a surprisingly advanced level of technology. Furthermore, in order to procure the materials for the road, several different species of tree had to be felled, debarked, and split. This suggests that the builders possessed high quality tools, and that they knew the differing properties of various roundwoods. It appears also that the builders were privy to the finer points of lumbering, maximizing the amount of wood extracted from a given tree by slicing logs of large diameter radially and logs of small diameter tangentially. Studies of the Sweet Track further indicate a high level of social organization among its builders. This is supported by the observation that the road seems to have been completed in a very short time; tree-ring analysis confirms that the components of the Sweet Track were probably all felled within a single year. Moreover, the fact that such an involved engineering effort could be orchestrated in the first place hints at a complex social structure. Finally, excavation of the Sweet Track has provided evidence that the people who built it comprised a community devoted to land cultivation. It appears that the road was built to serve as a foot-path linking two islands―islands that provided a source of timber, cropland, and pastures for the community that settled the hills to the south. Undoubtedly, the discovery of the Sweet Track in 1970 added much to our knowledge of Neolithic technology. But while study of the remains has revealed unexpectedly high levels of engineering and social organization, it must be remembered that the Sweet Track represents the work of a single isolated community. One must be careful not to extrapolate sweeping generalizations from the achievements of such a small sample of Neolithic humanity.
radially 放射状に tangentially 接線方向に