Some say it is the mystical Hill of Uisneach – burial site of the Earth goddess Ériu and the Sun god Lugh, seat of the High Kings, and birthplace of the original Bealtaine, the pagan fire festival marking the start of summer.
Others say it’s on an island in Lough Ree – the Lake of Kings – a great inland sea on the mighty River Shannon.
This was a historic crossing point: the oak foundations of a 9th-century bridge, 400 feet long, were discovered here only a decade ago.
(“Esker” is from an old Irish word eiscir, meaning "ridge". Formed more than 10,000 years ago during the last Ice Age – raised up, dry underfoot and relatively level – the eskers were used as communications routes for millennia, providing safe passage across the wetlands and bogs of Ireland’s historic heartlands. Pilgrims and hikers still walk them today.)
The Shannon was already an important trading route when Ptolemy mapped it in the 2nd century.
The ancient woodlands and myths of river gods go back further still. Legend has it that Síonnan, granddaughter of Lír, Celtic God of the Sea, visited the beautiful circular pool now known as the Shannon Pot, and angered the great Salmon of Wisdom living there. The pool overflowed, to become the source of this great river – and Síonnan drowned in the waters that took her name.
Iron Age peoples travelled this way: a short stretch of oak road built 2,500 years ago has been found close to the river in near-perfect condition, preserved by the special environment of the bog.
Then 1,500 years ago, early Christians founded monastic communities in remote reaches of the river, where the ruins of monasteries, oratories and round towers can still be visited, and peace can still be found. Vikings followed – sailing upstream into the heart of Ireland.
And in more recent centuries the history of Ireland has played out along this important thoroughfare – leaving evidence along its banks: Norman castles and Palladian mansions, and even Napoleonic Martello towers.
These days the Shannon and its huge lakes, tributaries and canals join Lough Erne to form one of Europe’s longest navigable waterways – a stretch of 750 km that is loved by the holidaying Irish and visitors from further afield for its watery and waterside pleasures.
No wonder – for surely this is the way to find the heart of Ireland.