Poundbury, from the 'Temple of Minerva', Maiden Castle, Dorset (Δοúνιον?)

Minerva/Athena on Maiden Castle? Ptolemy's Δοúνιον?

On Ptolemy and Geography 

 Dounion (Dunium) could also be Hod Hill, but I'll stick (provisionally) with the Mortimer Wheeler theory that it was Maiden Castle.

"Mortimer Wheeler (1943, 12) believed Dunium to be Maiden Castle because of its size and the later creation of the principal town of Dorchester nearby. Whereas Rivet and Smith (1979, 145) considered Hod Hill to be a better candidate because it lies closer to the latitude and longitude provided by Ptolemy...The Hod/Iwerne settlement is a strong candidate for a Late Iron Age oppidum or proto-town with trade links to the Gallic communities to the south and Dobunni to the north along the Stour. Hod is thought to be the location of Ptolemy's Dunium, the principal place of the Durotriges", Martin Papworth, The Search for the Durotriges, Dorset and the West Country in the Late Iron Age (2011).

On Hill-Forts - from An Inventory of the Historical Monuments in Dorset

Illuminated Manuscript at Vatopedi Monastery, Mt. Athos

From Mortimer Wheeler, 1943

Another suggestion (however far-fretched), as a possible derivation of the name:

Γυναικó-Καστρο

Athena, Attic Red Figure

Athena Cult

Athena and the Owl

Minerva Plaque Postcard (also in Wheeler, 1943, Plate xxxix, B, opposite p.334)

Sir Mortimer Wheeler (see ‘The Late Roman Temple and Its Enclosure’, Maiden Castle, Dorset, 1943, pages 72-79)

“In the absence of an inscription, the dedication of the temple is unknown and the variety of cult objects found in and near it is more puzzling than illuminating. Cunnington unearthed a small and indeterminate fragment of a bronze statuette approaching life-size, and a ‘feathered’ bronze votive plaque bearing a repoussé figure of Minerva and an inscription which is now too fragmentary for interpretation” (p.75).

(Edward Cunnington discovered and partially excavated the temple building in 1882; Mortimer Wheeler says that a plan made in 1882-1884, and Cunnington's manuscript notebook, are preserved in Dorset County Museum).

 Mortimer Wheeler observed that is not easy to interpret the cult and the various possible divinities worshipped at the Maiden Castle temple (Diana/Artemis is another possibility). Even the temple foundations themselves are open to interpretation as to the function of the building.

“It is relevant to recall the increasingly composite and transcendental character of paganism under the later Empire. It is not impossible to suppose that one than one element relating to nature-worship and rural craftsmanship found a home in this hill-top shrine within the last generation of Roman rule”.

In short, there is still no conclusive evidence that the temple was dedicated to Minerva, in spite of the discovery of the bronze plaque. The three-horned bull (Tavros Trigeranus) was a later discovery, as was the base of the marble statuette of Diana. Perhaps they were all worshipped by followers of the cult. There may be some people who prefer to entertain the idea that the temple might have been dedicated to the goddess Diana, with her statue gazing down disapprovingly, perhaps vengefully, at present-day Poundbury, for the loss of her hunting grounds.

Diana/Artemis

If we're permitted an element of romanticism, my vote is for Minerva/Athena (below)!

Temple reconstruction illustration, Peter Dunn, Historic England, here (English Heritage)

"Many unusual finds were excavated in both the temple and the hut shrine, including hundreds of coins and several statues, some imported from the Mediterranean. These were offerings brought to the deity who presided over the temple. This deity was perhaps the goddess Minerva, who was depicted on a bronze plaque found on the site. The lavish gifts and offerings show the flourishing wealth of the temple patrons" - English Heritage.

Excavations of Roman Temple and House,Site B, taken 8 Sept 1934 (Album Ref 7, 84)

Aerial photograph, Major George Allen.

 Ashmolean Museum

Some observations on the coins, contemporary with the building, found sealed in the primary floor of the cella, or in the nearby building, in the floor of the residence of the attendant priest:

John Cowper Powys, in his novel Maiden Castle, conveys well the unfounded theories or opinions that self-styled experts may express, when confronted for the first time by objects uncovered in an archaeological dig:

See also:

Mapping the Wessex Novel, Landscape, History and the Parochial in British Literature, 1870-1940, Andrew Radford, Bloomsbury, 2010 (pages 105-115 can be read online).

Perhaps the inspiration for the building of the temple was somewhat more mundane? Take Thomas Hardy's poem, Her Temple:

Her Temple

Dear, think not that they will forget you:
--If craftsmanly art should be mine
I will build up a temple, and set you
Therein as its shrine.

They may say: "Why a woman such honour?"
--Be told, "O, so sweet was her fame,
That a man heaped this splendour upon her;
None now knows his name."