Hadrian’s wall across Britain has left complex traces in the forms of trenches, pits, scraps of stonework which were not salvaged by later farmers and road-builders, and of course inscriptions boasting of what the dedicator had accomplished.
Geoff Carter, the archaeologist of Britain, is working on his theory that Hadrian’s Wall was first built as a dirt-and-cross-beams construction just in front of the later stone wall. At the eastern end of the wall the stone wall was completed, at the western wall the dirt-and-cross-beams wall survived as what archaeologists call the turf wall. He sees the deep ditch behind the wall as a construction trench for a stone road which was never completed rather than as a marker defining the southern edge of a military zone or a barrier to keep the soldiers’ horses, mules, and donkeys from straying.
If he is correct, the obvious explanation was that plans changed and the initial, very expensive plan for a 73 mile long stone wall and stone highway had to be scaled back. The evidence for this is post-holes, mounds of spoils and rubble, pollen analysis of the western “turf wall,” Statius’ description of how a Roman road was built, and a fort which was built over part of the wide ditch not long after its initial excavation. His theory also implies a considerable use of local labour to dig ditches and fell timber aside from the soldiers who left inscriptions on stone to commemorate their work.
While he decides what form of formal publication to make, he has blog posts at https://structuralarchaeology.blogspot.com/ and videos at Geoff Carter Theoretical Structural Archaeology (warning: Youtube).
He is convinced that he got caught up in an ideological battle between scientific archaeologists (like he sees his own work) and post-processural archaeologists (he tried to do a PhD on what kinds of building a set of post-holes could support, in a department which wanted him to talk about the cosmologies of prehistoric societies, and he just did not see a way to talk confidently about such abstract things using postholes and potsherds as evidence). Not being a Briton or an archaeologist, I can’t comment, but I like that his theory matches what we know about other monumental building projects in general (cathedrals often spend a few hundred years half-built) and Roman military engineering in particular (most forts and frontier defences were built first in earth and timber, and only later replaced with stone). So I hope he can find time to finish his book. In my experience, most scientists are open-minded about a new theory, as long as it is published as a formal argument with an accepted academic press or journal.