It's been a general trend to underestimate the achievements of people in ancient times. After all, unless there's proof that something happened, it's difficult to presume it did. And a bias toward modern technology means that just because something was possible, doesn't mean it was common and presumed to be too dangerous to be routine.
However I think it's one of those weird cliches that lay people come up with i.e. 'ancient people were dumb' to underestimate the achievements, that I've never come across in actual historians or people that know their subject. And so usually a historian starts with this cliche then proceeds to demolish it with their research!
Personally, I would modify those statements with a sadder note. That being, we tend to read research produced by those of our own culture/nationality. Additionally, many, perhaps even most historical researchers, no matter the subject area, tend to build their research off of the previously laid foundation of other individuals finished and published research, that is considered 'correct and accepted' as the foundation for their own... very often quoting or mildly rephrasing though regurgitating that old research verbatim. Finally, like it or not, a lot of older research contained a significant amount of cultural/racial/national bias. Failures, ignorance and so on, often considered 'as we expected.' Accomplishments often viewed as exceptions, rare occurrences where the primitive-lesser c/r/n overcame their inherent limitations.
When studying Native American history, and something more recent, WWII air combat over New Guinea which included earlier developments and required learning aircraft manufacturing practices, I was stunned by what I often discovered reviewing newer research by the accepted 'experts,' both new and previous.
First off, original works and publications, often written with scant facts available, typically tried to make sense of something alien to them, stated as fact, that X-Y-Z were knowns. Subsequent authors, took those statements, supposed facts, never questioning them and use them as the firm foundation for their work building upon it. And so it went... Researcher after researcher simply regurgitating what was originally done, then adding to it. Authors that softly challenged those standards as new information and understanding came to light, brushed aside.
I encountered this in GLARING fashion regarding the Japanese aircraft industry, Japanese Army Air Force structure, tactics and so on. When immediately shot down by the current experts, instead of conceding, with the ease of gathering and sharing information due to the internet, I was able to point out how each generation of publication literally, often exactly quoting, previous works all leading back to the original work-- I'm a novice at everything, yet, by not blindly accepting previous work, insisting upon starting from the beginning and using newer facts that have come to light, I was able to overturn a number of old accepted facts regarding the aircraft, manufacturing, structure, unit markings and tactics. More so, to gentlemen that are truly the accepted experts in the field.
Original research utilized by most new researchers, was very often generated by people that had nothing to do with the culture, looking from the outside in. Though lessened with work on Japanese air combat, there was a significant amount of racial/nationalistic bias/slurs/insults that was evident throughout. When it came to Native Americans, it was significantly worse. Lesser human (Japanese researchers) suddenly became observations of 'sub-humans' when researching Native Americans.
Point being?
1. Check to insure that the work is not simply built upon generally accepted facts that are never rechecked/challenged.
2. Be leery of any work that regurgitates previous work that is 'not' challenged.
3. Note the cultural bias of older work and consider the conclusions skewed (again, requiring that they be challenged).
If you start fresh, especially considering the ease with which information can be gathered now, you might be surprised at what you discover.
K2
I've been listening to some details of Roman trade, starting with the reign of Augustus, with India and communities south of the horn of Africa and that seems pretty well known. 
