Behind the cliff

What is remarkable about the tunnel system at Baia is that while the surface buildings show many signs of repeated repairs due to volcanic activity and rock falls, the interior tunnels show no signs of movement, nor cracks of any kind due to seismic events or pressure. Everything is in an extremely good state of preservation. This is because the mass of the rock and tunnels all tend to move together as one entity in a seismic disturbance.             

We have dropped below the surface buildings and have now entered what Doc Paget named the Great Antrum. It doesn’t quite run due east-west, as Doc Paget said, but it is close and it does seem deliberate that it the entrance is aligned on the volcano Vesuvius, across the bay.

Vesuvius, in line with the Great Antrum
Vesuvius, in line with the Great Antrum

The tunnel continues into the volcanic crater wall in a perfectly straight line for 124.5 metres (408 ½ feet), maintaining its narrow width and a height of about 1.8 metres. There are centuries of crystalline deposits on the floor, so the height is now somewhat reduced from the original. At the entrance, where the excavators dug down to bedrock, the height is about 2.5 metres (Over 8 feet).

The South Stub

The first feature of note we encounter on entering the tunnel is a very low short side tunnel to the left (south). It was mentioned in passing by Doc Paget, but left un-named. For want of a better description, we have been calling this feature among ourselves the South Stub. The shelf beyond it once had a Roman pipe sitting on it.

The South Stub side passage
The South Stub side passage
Looking into the South Stub
Looking into the South Stub

There are square recesses cut into either side near the entrance. This short tunnel, as far as we know, is blind, nowhere to go. Was there some kind of barrier across the entrance? This tunnel is so low that it suggests only an animal could exist here. 

What function for a simple steam channel for a Roman bath could this serve?

You are here

Under the ground and starting our descent

The Entrance

A last look at the entrance
A last look up at the entrance and a curious Trick of the Light

Behind the Original Entrance

A step backwards and we find ourself looking at the pipe behind The Original Entrance
One step backwards

We find ourselves looking at the pipe behind The Original Entrance. The pipe has a cemented drainage lip. It’s more likely that condensation from the Roman bath dripped out of here than that steam went in.

Supporting the Roof

The old Cliff line

The point where the tunnel originally started is clearly visible within the Great Antrum. In the Roman phase arched tiles supported the unstable material of the later rockfall.

Notched tiles support each other
Notched tiles support each other
The top picture shows the junction where the original entrance into sold rock meets Roman structure after rockfalls.

The Pipe Shelf

Looking back at the trench under the Greek Temple, we can see a shelf, low down, cut somewhat crudely into the side of the main tunnel. A Roman pipe sat here and seems to have simply ended.

Doc Paget thought this shelf once supported a pipe that channelled steam or hot water, across the passage and into the back of the hot room of the Original Entrance. 

This shelf extends too far beyond for this to be plausible. It seems doubtful any pipe here could have been anything more than yet another convenient drainage pipe, added much later.


The beautifully smooth cement render on the walls is called ‘cocciopesto’, formed of crushed brick and tile, mixed with lime mortar. In many places it is still intact, whereas in others it is blowing or crumbling off the walls.

The shelf upon which a pipe once sat
The shelf upon which a pipe once sat

The tile in the roof

The Roman tile, set in the roof
The Roman tile, set in the roof

Opposite the Tholos entry to the tunnel there is a Roman tile cemented into the roof, the red square seen in the top of the picture. It remains sealed in place.

Doc Paget recorded it but made no attempt to remove it.  He estimated that a tunnel above here would probably meet the tunnel in the south west corner of the Greek Temple where we see an unexplored opening that is blocked a short distance into it. What was its use? Where does it go?

The brick wall on the left is where the pipe at the back of the Tholos is set.

The Curious tile

A close up of the tile in the roof
A close up of the tile in the roof

The tile in the roof opposite the Tholos entry.

A tunnel above here probably exits into the back of the Greek Temple where we see an opening, but this tunnel has been deliberately blocked up with soil. Clearing this tunnel may reveal other features, as yet undiscovered.

Does a passage lead here?
Does a passage lead here, at the backof the Greek Temple?

The Tholos Pipe

Visible in the wall to the Tholos is the drainage pipe from the sudatorium on the other side.

Another view of the same hole, looking towards the entrance.


Our exploration of the area just behind the cliff entrance is now complete. Take a last view of daylight, you won’t be seeing it again for some while. Let us continue on our journey to the underworld…

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