Seamus Heaney and I were friends for 50 years. When he sent me and my wife a copy of Opened Ground (his Selected Poems 1966-1996) he inscribed it with these words from his poem Alphabets: "writing our names there".

I realise that I am now one of a multitude of friends and admirers. But that inscription – from a poem that affirms the power of poetic inscription – is validated, I like to think, by the poem he contributed to my 70th-birthday Festschrift. Here he remembers the mid 1960s, and expeditions with our wives in his blue Volkswagen around Co Down. After referring to us both as “fathers and sons”, he ends:

The pair of us, grandfathers too,

More pastoral / lyrical than epical,

Inclined to scry the gloom for what might gleam

As when a seal’s head rose and streamed and shone

For four of us, walking the harbour wall

In the sealight of Ardglass.

In a way I was introducing Seamus to Co Down, drumlin country, Strangford Lough. The Peninsula is his wonderfully clear-sighted response: ". . . things founded clean on their own shapes, / Water and ground in their extremity".

Marie and Seamus reciprocated by bringing us to their home grounds: mysterious Ardboe, on the shore of Lough Neagh, its Celtic cross, the rooky trees around Marie's home; and the Bellaghy farm, plain and unadorned, where a great imagination was brought to life. Mossbawn: Sunlight puts me in mind of Vermeer. I have had these lines by heart since the first time I read them:

And here is love

like a tinsmith’s scoop

sunk past its gleam

in the meal-bin.

We were exploring Ulster’s landscapes and learning to write poems. Seamus, the only driver, was always ready to go. On St Patrick’s Day 1965 we climbed Slemish with a group of friends and flopped on the summit to smoke reviving cigarettes and gaze out over the Antrim plateau.

In 1968 Seamus and I again travelled around the North, joined by the folk singer Davy Hammond in a performance called Room to Rhyme. After a boozy night in Cushendall we dragged our hangovers through heather stands to the cliffs at Fair Head. Davy took off his shirt. We signed our names on it with a biro and, suicidally close to the windy edge, launched it seawards.

In his essay Cessation 1994 Seamus associates Room to Rhyme with a moment of historical hope, soon to be disappointed: "At that time, there was energy and confidence on the nationalist side and a developing liberalism – as well as the usual obstinacy and reaction – on the unionist side. There was a general upswing in intellectual and social activity, the border was more pervious than it had been, the sectarian alignments less determining. I remember in particular feeling empowered by a week on the road with David Hammond and Michael Longley in May 1968 when we brought a programme of songs and poems to schools and hotels and libraries in unionist and nationalist areas all over Northern Ireland. "

Seamus goes on to say that the title Room to Rhyme, taken from the opening verse of a mummers' play, "expressed perfectly the eagerness and impatience that was in the air at the time".

Last year, at the Royal Festival Hall in London, Seamus and I took part in a collective reading in support of the Enitharmon Press. I told him I had recently been rereading his early poems. “I think they’re miracles,” I said. “They’re from Bellaghy,” he said with a chuckle. “They’d need to be miracles.”

I first got to know this work on smudgy cyclostyled sheets at the Belfast Group. We all applauded the knowing enjambment of "nimble- / Swimming tadpoles"; frogs at the flax dam "Poised like mud grenades, their blunt heads farting"; the concrete music of the "bottle / Corked sloppily with paper" and, in Churning Day, "the pat and slap of small spades on wet lumps". It is as though the particulars of life on an Ulster farm are inventing a language for themselves – a dialect that our senses seem always to have known. In a barn on a hot summer's day something almost religious happens, something both visionary and matter of fact, flawlessly "formed":

A scythe’s edge, a clean spade, a pitch-fork’s prongs:

Slowly bright objects formed when you went in.

Working very hard and at a dizzy altitude, Seamus continued to produce miracles throughout his life. Years ago he met me off the Enterprise train. We went to a quayside Dublin bar, sat on stools and, over balls of malt, recited new poems by heart. His was The Harvest Bow, a poem about poetry, about poetry and life, about war and peace, about the fragility of art and of everything. This may be his greatest poem. It wouldn't be so powerful were it not so consummate, the art that conceals art. The bow is partly a metaphor for Seamus's complex and enduring craft: "wheat" that "brightens as it tightens twist by twist". The Harvest Bow came into my head when I learned of Seamus's death: the "frail device"

Like a drawn snare

Slipped lately by the spirit of the corn

Yet burnished by its passage, and still warm.

In his last collection, Human Chain, I am mesmerised by A Herbal, a sequence translated from the French (though most of it sounds like pure Heaney). I sense the essence of the collection in such lines as these about the poet having laid his "cheek / Against the rush clump / And known soft stone to break / On the quarry floor". Why is this so heartbreaking? The poet as boy and man, body and soul.

I hope that one day I'll be able to write an adequate elegy for Seamus. In the meantime I offer two brief poetic reflections on my long friendship with him and Marie. At the 2011 Bloomsday conferments at University College Dublin, a number of poets were being given honorary degrees. During the formal lunch Seamus asked me, "What's the Greek for boat?" In such scholarly company I, who would claim to be a translator of Homer, couldn't remember. I was mortified. Soon afterwards I wrote Boat as a kind of squib to ease my embarrassment, but the poem, I hope, reaches deeper than that. It anticipates Seamus's death (and my own). Marie wrote to tell me it had moved her to tears.

Six months later, having been invited to write a poem about a treasure in the National Museum, I remembered a brooch Marie often wears. It's modelled on the Broighter Boat, one of the most beautiful objects in the world, all sheen and intricacy, delicate as an eggshell. My poem The Broighter Boat is a gift for Marie. Now that Seamus has arrived in Ithaca, I want him to ease aside the stowaway and take his proper place as the "transubstantial / Imaginary oarsman".