Never An Iron Age Fort
Garn Goch is much older than Iron Age (in fact, about 2,000 years older), and the simple fact is that it just does not fit the model for an Iron Age fort, although at first glance you could well think it does.
Iron Age forts in Wales fall broadly into three categories:
small earthworks forts on steep sided hills with multiple rings of banks and ditches built and defended by local communities
promontory 'forts' above sea cliffs, often 'defended enclosures' with limited defences sufficient to put off robber gangs, or neighbouring farmers
large forts with massive, still visible, smooth sided walls and ramparts, such as Tre'r Ceiri and Garn Boduan, requiring huge person-power from a wide catchment area to construct, maintain and defend. Understandably, there are very few of these.
Garn Goch's location and size (700 x 220 metres - Coflein says 680 x 190 metres) mean it would have to fall into the large forts category, but it offers no evidence - none at all - of such massive walls or ramparts.
Even the strengthened western wall is a pile of stones that could never have been a proper wall with ramparts. At most, it was an Iron Age folly intended to scare off invaders coming up the Tywi valley.
Now, when something looks like a dog and barks it might give people a clue that it's not a duck. Many still insist Garn Goch is an Iron Age fort, despite its major feature - the massive long cairn - being Neolithic.
The origin of this dog-duck confusion is nearly 50 years ago when the then expert on Welsh Iron Age forts was asked, at the end of his long career, to do a quick survey of Garn Goch, and guess what? He concluded it was an Iron Age fort, despite compelling evidence to the contrary, and his own admissions that he couldn't explain various 'anomalies'.