Roughly 9,000 years ago, the island that is now Ireland was almost completely covered with ice, which didn't melt away until the end of the last European Ice Age. During this time the sea levels were also much lower, due mostly to the huge ice formations covering most of the landscape. Due to these low sea levels, Ireland and Britain were a part of mainland Europe, and there were no islands in the region at this time. Historians and archaeologists believe that Mesolithic stone age settlers arrived in Ireland around 8000 BC, however very little is known about these people, and whether or not they are the direct descendants of the Modern Irish. These people spent about 4,000 years in Ireland as very primitive hunters and gatherers, and then eventually around 4500 BC, they began to master farming and agriculture. During this Neolithic Age, Ireland also saw a huge influx of cattle and sheep brought in from the Iberian peninsula.
In Ireland there is a place called the Céide Fields, and preserved there underneath a blanket of peat, is one of the world's oldest agricultural field systems. The archaeological evidence from this field suggests that the farming structure there dates to roughly 3500 BC. Some experts have gone so far as to claim that this is the oldest advanced human farming site in the world. What the field holds, are small dry stone walls, which are thought to have separated different crops of wheat and barley. These ancient stone age structures were discovered in the 1930s, when a schoolteacher Patrick Caulfield pealed away some of the turf to use as fuel. Today preservation of the site remains a very large challenge, but methods have been devised to keep the old structures intact, and away from the harsh climate. Aside from the farming structures themselves, there are also a number of very old tombs in the area, many of which haven't been fully explored or studied.
The Bronze Age began in Ireland around 2500 BC, with major technological innovations being made with the mastering of metal. Around this time huge inventions were discovered, such as the wheel, oxen harnesses, alcohol production methods, textile weaving, and many others. This time period saw not only a huge demographic growth spurt arise from the greater availability of food, but it also marked the time at which warfare became fairly commonplace on the island. With the mastering of metallurgy, came the production of new and deadly weapons, such as swords, daggers, spears, and metal arrows. With these newly discovered weapons and the advancement of food production methods, the early man of this time turned towards the ideas of conquest and empire building. The rocky soil in Ireland has produced some exquisite and extremely well preserved artifacts from this time period, many of which can be seen throughout Ireland's national museums.
With the arrival of the Iron Age around 800 BC, came the era of Ireland known as the Celtic period. It is still not known how many people inhabited Ireland during this time, however starting in the 8th century BC, wave after wave of Celtic invasions took place on the island. There were roughly 800 years of Celtic invasions, which would lead many scholars to believe that the native inhabitants of the time were very small in number, as there did not seem to be a huge amount of resistance to these invasions. By the 1st century BC, most of the Celtic invasions from mainland Europe had stopped, and Ireland was divided into five separate Celtic kingdoms. Some scholars believe that these five kingdoms were the result of gradual cultural diffusion, as opposed to warfare and conquest, but there is substantial archeological evidence to suggest that these times in Ireland were particularly violent, and plagued by warring tribes.
