History
Around 1200 to 1000 BCE, the most dominant iron-age warriors were the Celts. Ranging all over Europe, from the British Isles to Hungary, the Celts forged tough swords made of iron and backed with a ferocious tenacity that allowed them to dominate for centuries.
In the 4th century BCE, Celtic raiders defeated the armies of Rome and sacked Rome itself. Up until that time, Roman soldiers were trained and fought in the Bronze age Greek fashion; using phalanx formations, bronze spears and rounded shields. After that humiliation, the Roman army underwent a dramatic change by abandoning the outmoded fighting styles of the Greeks and Etruscans and adopting their version of the Celtic sword which they called the "gladius hispaniolis" or simply the "gladius." In addition to the new sword, new tactics, armor, and shields allowed the Romans to wipe out the Celts and dominate the Mediterranean for centuries.
Significance
Early iron weapons were soft and easy to bend. Comparatively, Bronze was stronger, held an edge longer, and was considered a more sophisticated weapon. Unfortunately, bronze was an alloy of copper and tin; two resources that were rarely found together and often had to be imported. Iron, on the other hand, is present in great quantities throughout the world. After working with refining and forging techniques, iron began to become harder, in essence becoming early versions of steel. These new iron weapons were stronger than bronze equivalents, and became more readily available (after early iron mongers and miners knew what to look for). The result was an adaptation of earlier weapons to the new iron technologies. Everything from arrow heads to armor began to be crafted out of iron, such as the above-mentioned gladius.
Geography
The presence fo weapons made of iron was influenced by geography, For instance, eastern Africa is generally recognized as the original site of iron weapons, but was shortly followed by Asia Minor (the Middle East), Europe and Asia (including India and China). In North and South America, iron weapons did not appear in the native population until well after the appearance of Europeans in the hemisphere.
Some locations in Europe became known for the high quality of iron weapons produced. In India, for example, monsoon-powered forged heated the furnaces and produced carbon-rich iron weapons (called "Wootz" steel) soon after iron technology was introduced. Damascus, in modern-day Syria, melded two different qualities and types of iron into a weapon through hammering, resulting in Damascene steel which was both flexible and extremely hard. Toledo, in modern-day Spain, was also known to be a producer of high-quality steel swords in the late medieval era.
Time Frame
Iron weaponry was used from about 1200 BCE to the middle of the 19th century when true steel was created in England. While early steels were in reality irons hardened though the infusion of carbon into the iron crystalline matrix, steel incorporated other elements in addition to or in place of carbon; manganese, copper, vanadium, and other inclusions strengthen steel and give it different properties. Still, iron weapons such as swords, spears (or lances), and bayonets were used in the Spanish conquests of what is now called Latin America. In the Revolutionary war, bayonets fixed tot he ends of muskets were a dagger made of iron. And while early cannons were made of bronze, most sophisticated cannon technologies used up until the end of the Civil War relied upon iron foundry technology.
Significance
In the years before widespread use of iron (and especially iron mining), iron was considered a "holy" metal as it was often extracted from meteorites. King Tutankamun was said to have had an iron dagger crafted from one such meteorite. In mythology, iron took on magical properties as so-called "cold wrought" iron (iron which had not been subjected to fire) was said to slay any number of magical and supernatural beings including demons and fairies.
Linguistically, iron came to symbolize strength and determination. The term "ruling with an iron fist" for example meant an unbending use of force. Someone who is said to have an "iron will" or "iron constitution" is someone who is impervious to temptation or illness, respectively.
Historically, iron was also used to denote invincibility. The USS Constitution, which was made of American Live Oak, was nicknames "old ironsides" when British cannon balls bounced off the tough wood of the hull without major damage. Ships with wooden hulls that were reinforced with iron "scantings" (braces and plates) were called "iron clad" ships and were an intermediary step between all wooden ships and the modern navies which rely upon steel for their hulls.