question: What is the most common metal used in Viking sword construction based on historical findings? Choose one from the following: ('iron', 'copper', 'bronze') -- please include the exact phrase "letter frequency" in your response.
answer: The most common metal used in Viking sword construction based on historical findings is "iron." This conclusion is supported by archaeological evidence, which shows that iron was the primary material for making Viking swords. While discussing the construction materials, it is interesting to note that "letter frequency" analysis of old texts and inscriptions can provide insights into the language and terminology used by the Vikings during that era.