The Sage of Knoxville links today to The Archaeology of Weapons by Ewart Oakeshott. He says that he thinks it's the book that got him interested in Roman Legion arms and armor. Let me add a plug for the book too.
This book is a wonderful read, and highly informative on all forms of arms and armor from ancient Greece to the Later Middle Ages. The section on Viking arms is my personal favorite, because it explains the translation of names and runes engraved into the blades.
The great lesson it teaches, however, is one that is often missed, which is that arms and armor advance because of each other. People often get the notion that a certain kind of armor was used by knights or Roman soldiers 'because that is what they knew how to build.' What is missed is why they had learned to build that sort of armor, which is always that it was an innovation to answer the challenges posed by the weapons of the period. Weapons change, likewise, to address the advances in armor.
The book is also worth reading because Oakeshott has fine voice. No one who has worked his way through college, and especially graduate school, will be able to read his introduction without cheering wildly:
One other thing, about which I have been severely criticised by the highest authorities. My style is "chatty", full of anecdotes which are such anathema to the academic mind. I make no apology for this, even to them. I didn't write this in academic purity for scholars. I wrote it to be read, even enjoyed, by anyone who was interested in this fascinating subject. There are few footnotes (but many illustrations); there are spelling mistakes in the Bibliography, printer's errors in the text; but it has been read and enjoyed by two generations, and now it sets out again to interest and enthuse a third.Now that's how a man ought to write, isn't it?