| 11. | The area is also known for its passage grave discovered in the 1880s.
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| 12. | The hill is particularly important for the two possible passage grave structures atop it.
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| 13. | These symbols are also commonly used in passage graves found in Ireland and Brittany.
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| 14. | On Zealand the chamber of a passage grave on Dysselodden is quite the reverse.
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| 15. | Passage graves consisted of a central burial chamber, with a long passageway to the entrance.
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| 16. | Other notable passage graves are Knowth and Dowth, also in the Boyne Valley near Drogheda.
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| 17. | Heapstown Cairn was constructed c . 3000 BC and is believed to enclose a passage grave.
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| 18. | There is a kerb of limestone blocks around the edge and probably a passage grave underneath.
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| 19. | Later versions featured larger chambers, passage graves, which could be re-used multiple times.
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| 20. | The mound is described as a Linkardstown-type cist but may be a simple passage grave.
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