Farming was established in the area during the Neolithic period. This provided a surplus of time and resources which was spent constructing great stone monuments to the dead, such as passage graves, court carins and wedge tombs. There are hundreds of surviving examples of these dotted across the landscape, however the most famous Neothlitic monuments in Ireland are those at Brú na Bóinne - Newgrange, Knowth and Dowth. These tombs were constructed prior to 3,000 BC making them older than Stonehenge and the Egyptian pyramids. The site is believed to have been of religious significance and is decorated with megalithic art. Newgrange, the largest pre-historic tomb in Ireland, is most famous for its alignment with the equinoxes, when sunlight shines through a 'roofbox' and floods the inner chamber. In constructing the tomb the early settlers displayed an advanced knowledge of astronomy and a calendar system. However, a writing system would not be developed until the 1st century BC, with the emergence of Ogham.