The ranking would move if a witness to Polybius 3.49.6 or Livy 21.31.4 gave a river name other than a form of Isara, because the Island would move with it. The known manuscripts have been collated for two centuries and none does, but the Vatican Polybius has not been re-examined for this page and Cluverius's conjecture has never been tested against a fresh collation.

A find would move it further. A datable Punic or Iberian object, a coin of Carthage, a Numidian bit, an elephant tooth, from any col or its approach would outweigh every item in the table. None exists for any candidate. The Traversette fieldwork of 2011 to 2017 found none, and no comparable excavation has been made at the Clapier, the Savine basin or the Clarea headwall.

Ancient DNA from the mire could settle whether the churned bed is an army's. Host-specific sedimentary DNA from the churned bed, of the kind now routine in Alpine lake cores, that showed Equus in quantity and no ruminant signal at the right depth would make the Traversette deposit an army's, though still not one army's. A ruminant signal at that depth would point to livestock rather than an army.

A snow record for the third century BC would move the two leaders against each other. A reconstruction of the third-century BC snowline for the Cottian Alps 300 m below the modern mean would put old snow on the Clapier in late October and remove the Traversette's advantage on the snow item; one 200 m above would remove the Clapier's partial claim to the snow altogether.

A finer terrain model could change the Clapier's view. The view test was run on a 90 m surface. A 5 m model of the Clapier ridge and the Clarea headwall could open or close the Clapier's sliver of plain; it cannot close the Traversette's 63-degree sector.

Reading Walbank and de Beer in full could change the weights. The principal modern commentary and the principal modern case for the Traversette were read only in part (see below). An argument in either that this page has not met would change the weights, though probably not the ranking.

Most of what this page says has been said before. That the Isère reading of the Island, the Allobrogian ambush at the mouth of the Maurienne and the Clapier's summit plateau fit Polybius best was argued by Perrin (1883), Azan (1902) and Colin (1904), and was the conclusion, always hedged, of Walbank (1956 and 1957), Proctor (1971), Lazenby (1978), Lancel (1995), Hunt (2017) and Hornblower (2024), and of Kuhle and Kuhle's reply to Mahaney (2012). That the Traversette fits the view, the snow and the steep descent was argued by Torr (1924), de Beer (1955) and Prevas (1998). That the Grand and Petit St Bernard fail on the Taurini is Livy's own argument. That the mire's radiocarbon window admits several armies was said by de Galbert (2016), and that the Traversette has no summit camp by Hunt (2016). This page adds numbers to those arguments and shows which of them carry the result.

Five things are new here, as far as I can find, and all five are new analysis of evidence already in print. No manuscript, artefact, date or measurement is added to the record.

First, a computed viewshed for every candidate col, for its first 10 km of descent and for the ground within a walk of it, against a single definition of "the plains of the Po". Earlier claims for the view rest on eyewitness reports from particular days. The result is that only the Traversette and, marginally, the Clapier see any plain from the col or the descent; the Mont-Cenis has a half-percent sliver from three cells on the ridge above it, and the other cols see none.

Second, a recalibration of all fourteen published Traversette dates against IntCal20 with a statistical test of the "bracketing" pair; the finding that nothing in the published age model's own output places the bed in 218 BC, and that its "firmly" and ">95%" rest on an agreement index read as a probability; the finding that the model table's modelled columns are inconsistent with its own agreement indices; and the observation that at this point of the calibration curve no radiocarbon measurement could separate 218 from 207 BC, or from any year between about 380 and 150 BC. I found no published statement of this arithmetic.

Third, the textual point that the name Isère stands in no manuscript of either author and is Cluverius's conjecture of 1624 in both, the Livian manuscripts pointing to Sarar or Arar and the Polybian to Skaras; and the observation that the Livian "1,000 feet" of the landslip is a Renaissance restoration of a corrupt line, not a manuscript figure.

Fourth, the demonstration that Polybius's two totals, 1,400 stades to the ascent and 1,200 for the crossing, cannot both be satisfied by any single line over the real terrain, so that neither total can be used against a candidate; and the observation that 1,200 stades equals fifteen days at the 80 stades a day of the preceding stage.

Fifth, the evidence model itself, with its shared-source correction, its leave-one-out test and its named sceptical scenarios, which trace the disagreement between the Clapier and the Traversette to three cells of the table, the practicability judgement, the Allobrogian ambush and the Island.

I have not been able to check the second and fourth points against Walbank's commentary or against the recent Italian literature, which were not accessible; a specialist may know a prior statement of either.

Several books were not read in full: Walbank's Historical Commentary on Polybius I (1957) and his 1956 article in the Journal of Roman Studies; de Beer's Alps and Elephants (1955) and Hannibal's March (1967); Prevas, Hannibal Crosses the Alps (1998); Hunt, Hannibal (2017); Lancel, Hannibal (1995); Hoyte, Trunk Road for Hannibal (1960); Seibert, Hannibal (1993); Proctor, Hannibal's March in History (1971); Mahaney, Hannibal's Odyssey (2008); Kuhle and Kuhle's two Archaeometry papers; Mahaney's Wiley papers of 2010, 2013 and 2019. These were obtained only as abstracts, search-inside snippets or library catalogue records, and their arguments are known here through the open literature and one another. Where the page attributes a view to one of them, it is from those secondary reports.

The editions are second-hand at two points. Livy's Latin was read in Foster's Loeb text as transcribed on Wikisource, with the Oxford apparatus from scanned pages; the Puteanus is lost for this book and the manuscript readings are taken from the Oxford editors. The Polybian apparatus for 3.49.6 is known only through Schweighäuser and the Oxford editors, since the Teubner editions print none at that point.

The terrain model is coarse, at 90 m. It can say that ground of the kind Polybius describes exists on a descent; it cannot say that a particular ledge or its landslip existed in 218 BC, and its col heights are up to 35 m low. Route lengths are valley-floor lengths and are lower bounds by perhaps 5 to 15 per cent for the gorges the ancient track would have climbed around.

The snow bands are judgements. The bands for old snow at each col come from the modern snowline and the glacier record rather than from measurement; no autumn snow-patch series for the southern French Alps was found, and no temperature reconstruction fine enough for one decade of the third century BC exists.

Nothing here has been checked on the ground. The Clapier's "white rock", the Clarea headwall, the Savine plateau and the Combe du Queyras are known to this page only from the model and from others' descriptions.

The model is a set of judgements, one for every likelihood range. The shared-source correction is a rule of thumb rather than a derivation; the two extreme treatments bracket it and are shown.