What is the oldest road tunnel in the world?

Question

At the Furlo Pass in the Apennines, the Via Flaminia passes through a tunnel built in 76 - 77 AD during the time of Emperor Vespasian, replacing an earlier tunnel.

The tunnel built during the time of Vespasian. Attrib: By AlMare (Own work) [CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons

This earlier, smaller (first) tunnel is "apparently of the 3rd century BC" according to the Wikipedia articles on Tunnels and the Via Flaminia, with the former article stating this is "one of the first road tunnels" (my highlighting). The article on the Furlo Pass states this smaller tunnel dates "from Etruscan times", as does the article on the Apennine Mountains

Did the Etruscans really build a tunnel here and, if so, is it the first known road tunnel built?

If not, what is the earliest known road tunnel built under or through a natural formation (i.e. not under or through a man-made construction)?

EDIT

In his answer, Alex makes the valid point that it is not exactly clear what a road is. There are various definitions depending on what source one looks at.

• Merriam-Webster has "an open way for vehicles, persons, and animals"
• Oxford offers "A wide way leading from one place to another, especially one with a specially prepared surface which vehicles can use" (Collins and Cambridge have similar definitions).
• Wikipedia: "A road is a thoroughfare, route, or way on land between two places that has been paved or otherwise improved to allow travel by foot or some form of conveyance".

For the purposes of this (historical) question, any of the aforementioned definitions are acceptable. However, I would exclude tunnels built for mining.

Answer 1

There is a tunnel under a mountain in Samos built around 530 BC. It is described by Herodotus, book III, 60. In 1882 a tunnel which matches Herodotus description has been actually found. It is one kilometer long and 2 times 2 meters in cross section, so its dimensions suggest that people walked through it.

What is especially amazing about this tunnel is that it was excavated from both ends and the parts of the tunnel met under the mountain almost exactly (but there is a visible small mismatch). This is mentioned in Van der Waerden's Science awakening, as an indication of high development of geodesy at that time. One cannot see the exit point from the entrance point on the surface because of the mountain in between.

Van der Waerden also mentions for comparison a tunnel excavated in 700 BC near Jerusalem, as an example of much lower level of technology. In 700 BC they knew nothing better than to make vertical wells to the surface to control the course of the tunnel, and still the result is about 2 times longer than a straight tunnel would be. (In the Samos tunnel such a method was not feasible because of the mountain above the tunnel.)

But in general, these questions of the type "who was the first", or "what is the earliest" are hard to answer because "there is nothing new under the Sun", as Kohelet (Ecclesiastes) already knew.

It is also unclear whether these tunnels qualify as "road tunnels" and what is the exact definition of a "road tunnel". People certainly could walk and walked through them, though the primary purpose of the Samos tunnel was water supply.

Answer 2

There appear to be two candidates which can definitely be considered for oldest road tunnel in the world, and a couple of others which are older but may be disputed. Roughly in chronological order, they are as follows:

1. The Euphrates Tunnel (circa. 2180 to 2160 BC, a little less than 1 km long). This has the most dubious claim as it was probably a passageway or pedestrian tunnel (rather than a road) under the Euphrates for private, royal use. Although nothing remains of it, it appears to have been a remarkable technological achievement and is described by Herodotus and Philostratus of Athens, among others (but details vary, and there may even have been more than one tunnel). This article quotes extensively from ancient sources about how opencast tunneling was used in the construction.

2. The Etruscan tunnel at the Furlo pass (circa. 450 BC, length unknown, but probably less than 40 metres). Umberto Marini, in Gola del Furlo (a brochure published by the Provincia di Pesaro e Urbino) credits the Etruscans with the first ever road tunnel:

In 450 BC, to get past a boulder that hand [sic] blocked the pass (during the floods of the Candigliano River), the Etruscans – aided by chisels, water, fire and vinegar – perforated the boulder thus giving rise to the age of road tunnels

It is unclear if this 450 BC tunnel is the same as the Etruscan tunnel near the later Roman tunnel mentioned in several Wikipedia articles: the Wikipedia pages mention either 3rd century or simply Etruscan times. There are some visible remains but whether it was a proper road tunnel or just a pedestrian passage is also unclear. However, even if the Etruscans cannot claim bragging rights to the first road tunnel, they can certainly claim credit for showing the Romans how to do it.

3. Grotta di Cocceio (aka the Cocceius Tunnel, circa. 38 to 36 BC, almost 1km long). This definitely qualifies as a road tunnel and was constructed under the supervision of the architect Lucius Cocceius Auctus who was also responsible for the Cripta Neapolitana (see below) as well as (probably) a tunnel on the island of Ponza.

Source: Napolipiu.com

It connected Lake Avernus with Cumae and was constructed using counter excavation (from both ends) with shafts. This is the longest road tunnel the Romans ever built.

4. Cripta Neapolitana (circa. 37 BC, 705 metres long). Also definitely a road tunnel, it runs from Naples to Pozzuoli and the building technique used was counter excavation. It was 3 to 4 metres wide and 3 to 5 metres high and made it easier for the Romans to move troops between Naples and the Phlegrean Fields.

By Mentnafunangann (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Impressive though this tunnel is, Seneca seems to have had a rather dim view of it:

Nothing is longer than this dungeon, nothing more gloomy than these torches, which don’t let us see through the darkness…even if the location had light, the dust would swallow it up…