This is a cool question, and as someone who has spent a lot of time (and a dissertation) putting sites back together from Depression-era excavations, I think I might have some relevant observations...

First, it's important to remember that people have never really been content to leave stuff alone if it was interesting enough, or if it could make them money. We often talk about the looting of the Egyptian tombs, but that's just one of the more apparent examples. Ancient buildings and sites are often fragmentary not strictly because of the passage of time, but because it's easier to recover building stones and brick from piles of rubble than it is to quarry and shape it yourself.

Added to that the fact that people of later cultures have often repurposed ancient sites for other needs, reshaping them to whatever their then-current requirements were. We often find that the clay and fill used to build ancient earthen mounds in the United States contains remains from cultures far older than those who built the mounds. And radiocarbon dates taken in sequence from bottom to top in some ancient constructions may well show reversals characteristic of a previous site literally having been dug up (and "reversed", as the stuff on top is deposited at the bottom of the new construction) to build new sites or monuments.

So it's not as if archaeologists (or the ideological forebears of archaeologists) are the only ones we have to worry about. People have been destroying the archaeological record since it was new.

The point of the above is to contextualize the idea of archaeological site destruction. Yes, it's incredibly unfortunate when folks in the 18th, 19th, and early 20th centuries tore up archaeological sites, but one way to look at it is that without their (usually very destructive) efforts we might not have anything remaining from those sites.

Of course, we should distinguish between the people who were really just glorified looters, and those who were actually interested in deriving some kind of information about the past. The days of "early archaeology" are full of the former, and contain fewer of the latter. However, there were plenty of well-intentioned people digging into sites in ways that would make modern archaeologists cringe, but who were doing so because they legitimately wanted to learn about the origins of those sites.

You can look to people like Japetus Steenstrup and Jens Jacob Worsaae, a pair of Danish scientists who were very interested in whether or not the massive shell middens along the Danish coast were natural or of human origin. They dug into them without much control, but their observations-- large quantities of human tools, food waste, etc.-- confirmed that they were in fact cultural in origin. That was a major step forward, even as it destroyed large amounts of information that we would love to collect today.

Archaeology is destructive, but for every bit of information lost, we have to consider what was also recovered. And not only direct information or artifacts, but also what progress forward was made in the methods of archaeology. Digging / excavation, recording, development of an understanding of what information could be collected, and how best to do so.

So while we have lost a great deal of the past as a result of the work of early archaeologists, we nevertheless see the field's development and advancement as a direct result of their efforts.

It's also important to recognize that we have a lot of information from the writings of these early archaeologists, and so even if they didn't save, draw, or document everything in specific terms, we can "dig" back through their writings for clues as to what else they may have observed that at the time didn't seem important enough, but in retrospect gives us clues about sites we could never look at today.

Fast forward many decades to the early 20th century in North America...

One of the most extensive pushes for archaeology-- and especially for large-scale archaeological excavations-- came during the Great Depression in the US. The federal government essentially funded an enormous number of public works projects, and thanks to historic preservation laws passed in the early decades of the 20th century, the government felt some measure of responsibility to first do archaeology in the areas that would be destroyed, or flooded.

Huge numbers of significant archaeological sites were dug up during that period. And the documentation and materials from those excavations mostly ended up in state universities and other curation facilities around the country.

A lot of folks have been reluctant to work with a lot of that material, because archaeologists in the early 20th century approached excavations differently than folks in the post-radiocarbon era did. They discarded a lot of stuff that we keep and focus lots of work on these days-- the remains from making stone tools, animal bone that today we use to understand diet-- and that's kept us from being able to use those sites to answer some of the important questions we ask of sites today.

But when you really start poking around in their records, you find that they also recorded an incredible amount of information, much of it very detailed and internally consistent. I've literally reconstructed entire sites' stratigraphy digitally based on the 3-dimensional coordinates of artifacts that were recorded when the sites were dug up. It's amazing.

As 21st century archaeologists, we sometimes look back at the work of earlier archaeologists and might cringe a little, but we also need to recognize that they were working with a different set of information than we have. They had, for example, no knowledge of radiocarbon dating (it didn't exist as a practical method until the 1950s), so why keep materials that can be used for radiocarbon dating, but otherwise seem mostly useless / a waste of space.

Archaeology is very much dependent on trial and error, and it's largely reactive rather than proactive. A new method of dating inorganic artifacts could be developed tomorrow that would let me precisely date a fragment of fire-cracked rock (which is ubiquitous on archaeological sites in many parts of the world) to within 5 years of when it was used.

That would be a major discovery and would reshape how we build chronologies. Especially if it were inexpensive.

But that method doesn't exist now (see edit below), and fire-cracked rock is heavy, usually occurs in significant quantities, and doesn't really tell us much else of use. So most archaeologists don't bother to save it, we count it and throw it away.

Archaeologists living in the hypothetical era of fire-cracked rock dating would look back on us in the pre-FCR-dating era and cringe at the information we threw away.

I hope that, if that (or any number of other potential advances for which we have little to no warning of currently) ever comes to pass, we're not judged too harshly.

---

edit: I should note that, in point of fact, there are methods that FCR could be dated. The problem is that they rely on precise methods of data collection-- not only does the material have to be collected, but a sample of the sediment in which it's embedded also has to be collected-- and most archaeologists today aren't really digging sites in a way that allows for that. Furthermore, most of the archaeology done in the US is done by commercial firms, and the dating method-- luminescence dating-- is still not as widespread or as fully integrated into methods as radiocarbon dating, which has been refined over the last 60 years.

Some people are using it, but it's still at the stage where if it's being used, we're also using radiocarbon to cross-check the results. So it's not there yet. And there's no good way yet to just take a piece of FCR willy nilly, without any sediment sample, and get a date.

There is a political element to this question owing to the National Historic Preservation Act of 1966 and related laws that makes it somewhat awkward to answer, but I won't dwell on that here, I guess relegating my answer to at least 20 years ago, though truth be told...

Anyway, the short answer is this: as of 20 years ago, it was still a mixed bag.

But, what does this mean? Well, the other answers make good points about advances in methodology. There's also a lot to be said, at least in North American archaeology, about federal programs during the Great Depression, and their effects on archaeology as a profession. But, still, there are two other issues (a million, really) that need to be addressed.

First, once we have the data, what do we do with it? I mean, how do we store it in a way that is accessible to researchers and land managers? Digging up the stuff is one thing, if we just throw it away after, we might as well just have bulldozed it. This, then, is a question about data science and data stewardship. Here there were important advances in the mid twentieth century. Archaeologists like Jesse Jennings developed the Intermountain Antiquities Computer System (IMACS) to standardize and store data in an easily accessible way, or that was the idea anyway. Other systems, like Robert Heizer's in California, were developed concurrently, though I'm less familiar with them. Jennings also led the surveys and excavations related to the Glen Canyon Project in the 1950s, a seminal event in the development of archaeology as a science (Jennings 1994, Accidental Archaeologist). The establishment of State Historic Preservation Offices by the National Historic Preservation Act of 1966 also proved critical. These are state agencies designated with being something like the institutional historical memory of each state, keeping records of each historic site recorded on public land (the National Register Bulletin is a good source of information on this).

Second, and equally important, what makes the data worth collecting? Advances in methodology allow us to extract and preserve more information through excavation, but does it really matter whether the projectile point you unearth lies on its dorsal as opposed to its ventral side? This is a touchy, n-dimensional question with no easy answer, but we can point to two sources of guidance. On the one hand, there is legal and political guidance. The US Code of Federal Regulations, specifically 36 CFR 60, defines historical significance according to four criteria: A. association with an event related to important themes in US history (e.g., the first colonists 15k years ago and the Civil War), B. association with important persons or places (e,g, if John Wayne got drunk in your pool), C. the work of a master (think a Frank Lloyd Wright house), and D. data potential (will additional excavation lead to important insights?). The history of how these criteria were established is an interesting story in its own right, but the important point here is that they established legal guidelines (along with 36 CFR 800) regarding when excavation was necessary and how its scope and limits should be determined. This is now done in consultation with land managers from federal and state agencies.

At any rate, Criterion D (data potential) leads me to the next source of guidance re: significance, specifically anthropological theory. The problem, in this context, is that a lot of archaeology (twenty years ago, I guess) was still largely an inductive enterprise, driven more by an interest in answering the what and how rather than the why. Thus, excavation was not organized around testing hypotheses deduced from a general theory of behavior. On this front, it was the work of archaeologists like the infinitely controversial Lew Binford that introduced a deductive approach to archaeology and excavation. In the 1960s, this was called the New Archaeology, also sometimes Processual Archaeology. While Processual archaeologists are not perfect - who is? - they did drag the field kicking and screaming into the scientific method, most of it anyway. Science is a complicated human affair, and variability in resource quality and data management was pretty large then (and still is now). Hence, my short answer: a mixed bag.

The definitive source on these issues is Bruce Trigger (2006). A history of archaeological thought.

Final caveat: no archaeologists is perfect, but they mostly have good intentions, and they go to heroic efforts to preserve the physical media that store the collective memories of our species.

u/han_dies_01 wrote:

The point of the above is to contextualize the idea of archaeological site destruction. Yes, it's incredibly unfortunate when folks in the 18th, 19th, and early 20th centuries tore up archaeological sites, but one way to look at it is that without their (usually very destructive) efforts we might not have anything remaining from those sites.

​

In addition to agreeing with everything the other posts say about how sites can be degraded by successive recycling, reliving in the area, etc., over the hundreds or thousands of years since they were in use, it's worth adding a note to emphasize the emergence of new forms and dramatic intensification of old forms of site destruction that the modern era has brought. Often the progression of the modern era has been accompanied by a drastic (and continuing) wave of destruction at sites that might have lain in relative peace since their initial destruction or abandonment for two or three thousand years but were much more heavily degraded, if not all but obliterated, over the past century or two for reasons not directly, if even at all, related to archaeology good or bad. Just the introduction of mechanized agriculture has obliterated ancient remnants that you used to be able to find right under the surface, or even see on the face of the land, over huge tracts of the Middle East in just the last few decades - you might have been able to pick out by eye from the air, or even from the ground, the outlines of a three thousand year old dirt road leading to your ancient Syrian village in 1950, that now is all plowed up and gone.

​

Even before tractors and plows started churning up the land in the Middle East, modernity wasn't being kind to archaeological sites, as noted, by, e.g., Bagnall in 1993 (Egypt in Late Antiquity) writing of town and even city sites of Hellenistic and Roman Egypt:

​

Probably the large majority of those [sites] still extant a century ago were destroyed in the first two decades of the twentieth century.^(6)

​

Bagnall is not talking about destruction by archaeologists, but largely by people digging for sebakh (earth enriched from the bricks of ancient buildings, used for such things as fertilizer and saltpeter), with assists from other largely new types of off-record exploitation (like artifact and papyrus hunting) and from sheer increased area taken up by modern constructions that grow alongside rapidly increasing populations.

​

Bailey (Sebakh, Sherds and Survey in The Journal of Egyptian Archaeology) collected together a bunch of descriptions of the fertilizer-out-of-ancient-bricks industry in action in Egypt in the early 20th century (and the desire to dig up ancient towns for fertilizer is not unique to Egypt, just particularly noticed and commented on there):

​

...The government itself sold off the rights to entire sites: the whole of the mound of Athribis 'was sold...many years ago, to a very rich and influential landowner, who sells the sebakh to various companies and private persons'.^(15) In 1924, the Antiquities Service, despite the antiquities laws, had great difficulties in ensuring its own rights. Earlier, in 1906, Gaston Maspero describes the attempted seizure by a wealthy proprietor of the whole site of Medinet Madi, the ancient Narmouthis, in the Fayum, for his own sebakh-extraction and agricultural purposes.^(16)

At Karanis, the University of Michigan excavators, from the start of their work in 1924, were required to accommodate the Daira Agnelli, a land company with a permit to remove 200 cubic metres of sebakh daily, and had to supply that organization with the soil that was archaeologically excavated. The entire centre of the ancient village had already been eliminated before the commencement of the excavations, and thousands of tons of sebakh, consisting of houses and their contents, were extracted by large and small groups of sebakhin, often using railways to carry off the earth.^(17) At Kom el-Hisn in the Western Delta,^(18) Georges Daressy in 1903 reports how quickly the mound was being removed by a land company entitled the Delta Light Railways, and in 1943 Abdeul Hamada and Mustafa el-Amir state that the mound was by then 'scarcely higher than the cultivated land surrounding it, and very few are the potsherds seen on its surface. Half a century ago it was 7 or 8 metres high...' Much of the material later than the Second Intermediate Period has gone.

​

So, upshot... It is true there are a number sites that happen to have been protected through the modern era except for the fact that they bear prominent scars from destructive early archaeology, which caused irrecoverable and sometimes totally needless, facepalm-level damage to a site that we otherwise still have today. It's difficult not to feel wry about some of that needless scarring.

​

On the other hand, nonarchaeological destructions are such that sometimes you'd wish quite hard that some nineteenth century archaeologists had gotten around to digging all over an old city mound and turned it over willy nilly to their hearts' content, if they would have only taken good notes and drawn a few pictures while they did, because then at least you'd have something where today there is a site in far worse shape than in their day, or else there is no more site at all and no archaeological record either.

​

Consequently there is no generally applicable line. At some sites eyes can be rolled at excavations from the 1930s, for other sites we can wish that if only they had excavated in 1830...