The table below weighs eight candidates against fourteen items of evidence. Six are the cols that have had serious advocates. The seventh is the Grand St Bernard, which had the Roman tradition on its side. The eighth, "another col", stands for the passes nobody has argued for at length, the Malaure, the Agnel, the Croix and the Autaret among them. The Mont-Cenis row covers both cols of its plateau, the Grand and the Petit Mont-Cenis. Each candidate starts with a prior, the share it holds before any evidence is weighed: an even 14 per cent, the Larche and the Petit St Bernard slightly less and the Grand St Bernard 6 per cent, because Polybius's own list excludes the Aosta passes. The prior hardly matters. With a flat prior, the same share for every candidate, the headline shares change by less than one point.

The fourteen items fall into five families. The nine Polybian items are the narrative: the Island, the ten days along the river, the Allobrogian ambush, the nine days to the summit, the view, the old snow, the broken descent and the three days to the plain, the arrival among the Taurini, and the 1,200 stades. Livy's Druentia itinerary is one item. The testimonia are two: Varro's order with Pompey's letter, and the Roman tradition of the Graian and Pennine passes. The Traversette mire is one. Practicability is one. For each item and each candidate the table gives a range, my estimate of how likely that evidence would be if this col were the pass. The best-fitting candidate sits near 1; a candidate the item nearly excludes sits near 0.02. The ranges are argued in the sections above. A reader who disagrees with a cell can change it in code/evidence_table.py and re-run the model.

The items are not independent. Everything in the Polybian family comes from one author working from one set of informants, and Livy's account of the same events comes down the same tradition, so he adds no second witness. Multiply the nine Polybian likelihoods together as if they were nine witnesses and the Clapier goes to 70 per cent. Collapse each family to one item instead, by taking the geometric mean within it, and the view, the snow, the descent and the Island count as one fact because one man reported them, though they are different facts. That treatment gives a near-flat result in which the Larche leads at 18 per cent, because it is an easy pass and Livy's Durance suits it. The headline run takes a middle course. Every Polybian item enters at half strength, as if the nine were four or five independent facts, and everything else enters at full strength. That run gives the Clapier 40 per cent, the Traversette 29, the Mont-Cenis 16, another col 9, and the rest 6 between them. Those shares are conditional on the fourteen items and on the ranges set for them. When every cell is sampled inside its range 20,000 times, the Clapier comes first in 65 draws out of 100 and the Traversette in 29.

Dropping items one at a time shows what carries the ranking. Remove the practicability judgement and the Traversette leads, 45 to 32; remove the Allobrogian ambush and it leads 40 to 31; remove the Island, or the ten days along the river, and the two are level at about 35 each; remove Livy's Druentia and the Clapier rises to 49. No single Polybian item decides it. The view and the snow are the two items that most favour the Traversette, and each moves it by only a few points, because the Clapier has a partial claim to both.

The scenarios in the table below put the sceptics' cases in numbers. If de Beer's Island at the Aygues is right, the Traversette leads at 54 per cent. If Livy's itinerary by the Tricastini and the Durance is trusted in full, it leads at 46. If Mahaney's deposit is credited as the authors read it, it leads at 55; if the Traversette is granted to be as practicable as any other col, at 51. If the view is a commonplace the Clapier still leads, but the Mont-Cenis rises to 24 per cent; if Polybius's old snow is a generalisation, the same happens. If his numbers are distrusted altogether, nothing much changes, because the numbers are the least discriminating part of the case.

The table can be read in two ways. One is that the Clapier is the best single answer on the evidence as it stands, weighed as the table weighs it, and that its odds over the Traversette are about seven to five, a long way from ten to one. The other is that the question is which valley, the Isère or the Durance; that the choice turns on a conjectured river name and on how far the word "Allobroges" can be stretched; and that once the valley is chosen the terrain picks the col with little doubt, the Clapier for the Isère and the Traversette for the Durance. I hold both readings. That is why the verdict at the top of this page calls the Clapier the leading candidate and says that several passes remain possible.