Architecture - Ancient

A more developed megalithic tomb is the passage-grave. Passage-graves consist of one or two burial chambers covered by a large earthen mound, with access through a passage from the edge of the mound. These tombs date from around 3000 BC. The best-known examples, Newgrange (see page 18), Knowth and Dowth, are located in close proximity to each other in the valley of the River Boyne near Drogheda. At Newgrange the mound is almost 11 metres high and 85 metres in diameter and the passage is about 19 metres long. The roof is constructed by corbelling, placing layers of flat stones one on top of the other, each layer protruding inwards over the one below. The passage-graves are the work of a well-organised and advanced civilisation. At Newgrange a small opening in the stonework is so designed as to admit sunlight to illuminate the central point of the burial chamber on 21 December, the shortest day in the year. Unlike other megalithic tombs, some of the stones in passage-graves were ornamented with geometric designs.

During the Bronze Age (2000-500 BC) smaller megalithic tombs appeared: these had burial chambers surrounded by stones on three sides and were covered by a wedge-shaped mound. However, most Bronze Age tombs were simple stone-lined compartments for individual burials.

The construction of large fortifications probably dates from the Iron Age (after 500 BC). Large circular stone forts were built, often on hilltops. One of the most impressive monuments of this period is Dún Aengus on the Aran Islands, a huge semi-circular stone fortress built right at the edge of high cliffs with strong defensive protection. Smaller ringforts, constructed of stone or earth, probably served as fortified dwellings. Another type of dwelling, the crannóg, was an artificial island of stone and wood constructed in the middle of a lake.