Grongar Hill is located in the Welsh county of Carmarthenshire and was the subject of a loco-descriptive poem by John Dyer. Published in two versions in 1726, during the Augustan period, its celebration of the individual experience of the landscape makes it a precursor of Romanticism. As a prospect poem, it has been the subject of continuing debate over how far it meets artistic canons.

The hill lies in the parish of Llangathen and rises abruptly not far from the River Tywi. The Ordnance Survey reference is SN573215 / Sheet: 159 and the co-ordinates are latitude 51° 52' 23.85" N and longitude 4° 4' 23.17" W. Its name derives from the Iron Age hillfort on its summit, in Welsh gron gaer (circular fort). At the hill's foot is the restored mansion of Aberglasney that once belonged to John Dyer's family and where he grew up from 1710. The area was important during the Mediaeval period of Welsh independence and from the 150 metre summit of the hill the ruins of several neighbouring castles can be seen; most notably "the luxurious groves of Dinevor, with its ruinated towers, present themselves with venerable majesty on the left; while the valley spreads in front....and the ruins of Dryslwyn castle, upon an insulated eminence in the middle of the vale."

The first version of John Dyer's poem appeared with a selection of others by him among the Miscellaneous Poems and Translations by Several Hands, published by Richard Savage in 1726. It was written in irregularly lined pindarics but the freshness of its approach was concealed beneath the heavily conventional poetic diction there. In the second section one finds "mossy Cells", "shado'wy Side" and "grassy Bed" all within six lines of each other; and in the fourth appear "watry Face", "show'ry Radiance", "bushy Brow" and "bristly Sides", as well as unoriginal "rugged Cliffs" and at their base the "gay Carpet of yon level Lawn".

Within the same year the poet was able to mine out of it the unencumbered and swiftly moving text which is chiefly remembered today. This was written in a four-stressed line of seven or eight syllables rhymed in couplets or occasionally triple rhymed. Geoffrey Tillotson identified as its model the octosyllabics of Milton's L'Allegro and of Andrew Marvell's "Appleton House", and commented that he "learns from Milton the art of keeping the syntax going". He could also have mentioned that Marvell had employed the same metre in the shorter "Upon the Hill and Grove at Billborrow", which takes its place in the line of prospect poems stretching from John Denham's "Cooper's Hill" (1642) through Dyer to the end of the 18th century.

Dyer's poem differs from most of these in that it is shorter, no more than 158 lines, and more generalised. Although the hill itself and the River Towy are named in the poem, the old castles on the neighbouring heights are not, nor is their history particularised. Instead they are made an emotional image and given Gothic properties:

'Tis now the Raven's bleak Abode;
'Tis now th'Apartment of the Toad;
And there the Fox securely feeds;
And there the pois'nous Adder breeds,
Conceal'd in Ruins, Moss and Weeds:

— Lines 77–81

From this contrast with their former glory, the poet says that he learns to modify his desires and be content with the simple happiness that his presence on the hill brought in the past and continues to do. The drawing of a moral is more a private affair, in the same way that the poet's contentment is a sincere personal response to the natural scene, rather than made the occasion for public lesson-drawing – still less is it, as in the case of the several later parson poets that adopted other hills, used for professional admonitions from their pulpit.