This was the great Irish poet Seamus Heaney in a unique context: in concert, alongside the renowned uilleann piper, Liam O'Flynn, in a live collaboration of words and music. It was the perfect embodiment of the Celtic Connections Festival which, in its sixth year, and with over 200 concerts across Glasgow in the next fortnight, is now the biggest winter arts festival in the country.

Even so, the appearance of Heaney and O'Flynn was something of a coup for the festival. Their show wasn't so much a honed act as an informal attempt to capture a moment of spiritual history, and at first Heaney's poems and O'Flynn's music seemed unrelated. But as the stately imagery and keening wash of the pipes progressed, it was clear that writer and musician were drawing from the same well - the darkness and light of personal experience and Irish history.

Heaney recited an early poem, from the 1966 collection Mid-term Break, about the death of a young brother. It seemed to glide into the shivering beauty of O'Flynn's Music of the Spirits - and it all began to make sense, Heaney's complex simplicity and sinewy detail serving as introductions to the laments and jigs. The six magnificent stanzas of Heaney's Keeping Going, about retaining inner freedom amid the 30-year hell of the Troubles, was a tribute to human dignity followed, appropriately, by O'Flynn's epic version of the ancient pipe tune, The Fox Chase, ending with a haunting lament for the fox and its lost freedom.

Celtic Connections may have over-reached themselves here, the pungent intimacy of this extraordinary performance sometimes lost in the vast hall. But the poet and the piper won through with the clarity and grandeur of their language.

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