Appearance and functioning

The lighthouse acquired a symbolic meaning in relation to the afterlife. This is evident, for example, from the relief on a sarcophagus with a ship approaching the lighthouse and a scene in a tavern (relief R04). We would expect to see two crew members sitting in the bar. The left person however is a woman, and apparently we see the couple for which the sarcophagus was intended. A mosaic in front of a tomb has the Greek text "Here is the end of sorrow", flanking the lighthouse (mosaic M10). In such cases an accurate representation of the lighthouse may not have been a primary concern of the artist. But also without religious symbolism the depiction may not be entirely accurate. There was no inherent need for that: both the artists and the people looking at their work could see the lighthouse with almost no effort. A partial, simplified or exaggerated representation could have corresponded to the artists' wishes. We must be cautious in using the visual evidence.

The height of the lighthouse

The numerous depictions of the lighthouse leave no doubt that it was an impressive monument. The ancient authors do not give us an indication about the height of the lighthouse. It seems that the lighthouse in Alexandria was more than 100 meters high, with a foundation of 30 x 30 meters. There are reasons to think that the lighthouse of Portus was a bit higher. First of all, Suetonius establishes a clear relation between the two towers, when he says that the lighthouse of Portus was "a very lofty tower after the model of the Pharos at Alexandria". It is not unreasonable to think that Claudius wanted to use the lighthouse to stipulate the supremacy of Rome. The lighthouse of Alexandria was famous because it was the highest building in the world. A Roman Emperor could hardly tolerate that the lighthouse of Portus and therefore of Rome would be lower. Although much admired, Egypt was in the end "just" a province, supplying grain to the capital. Aline Boyce may well be right when she suggests that the sinking of a ship that had been used for the transport of an obelisk and its use as part of the foundation of the lighthouse was not merely a technical operation, but also a symbolical deed. The lighthouse of Claudius must also have been more than 100 meters high. The fire could then be seen from a distance of about 26 nautical miles, almost 50 kilometers (so also in Rome).

Image: Portus Project.

The shape, number and height of the storeys

According to Stuhlfauth the lighthouse probably had four storeys: the lower three square or rectangular, the upper one cylindrical. The shapes can be seen clearly on several ancient depictions. On the ancient depictions we see three, four, five and six storeys. I am inclined to think that there were four storeys, including the cylinder. A higher number is seen on two mosaics. The first is in the Baths of the Lighthouse. This mosaic is of good quality, but one might argue that the tower was stretched for artistic reasons. The other mosaic is in the House of the Harbour Mosaic. On most depictions the storeys become lower towards the top. We might think of storeys that were 50 - 30 - 20 - 10 meters high. The first storey seems to have been very wide and high.

Materials used

The only direct evidence for the materials that were used comes from the drillings, for the most part in the foundation of the island on which the tower rested. The remains were found at a great depth, up to -15 meters, the ancient seafloor. The finds included basalt, "tufo lionato" (tufa turned black by water and called lapis ruber in antiquity), and sherds. The record is of course incomplete, because of the extensive plundering of the site over the centuries. Enormous basalt blocks were used for the northern mole, and can still be seen today. The walking level was there covered by travertine blocks. Pliny the Younger has described the construction of the harbour at Centumcellae, to the north of Portus, and mentions the dumping of large stone blocks to create an island (Epistulae VI,31).

Several ancient depictions show a net of horizontal and vertical lines on the floors of the lighthouse, suggesting the use of large stone blocks. The most obvious material to have been used is travertine. To what extent tufa blocks could have been used is something to be determined by engineers. Marble revetment is reported by Flavio Biondo in the mid-fifteenth century, but this could be an exaggeration. On the Torlonia-relief opus reticulatum seems visible in the interior.

Openings in the tower

The ancient depictions show four kinds of openings in the tower: large, arched openings, rectangular doors, rectangular or square windows, and short and long vertical lines. The latter must be high and narrow windows ("slit windows"). The long lines may be regarded as a representation of several of these windows. For the interpretation of these openings it is important to realize that the ancient depictions could well show different sides of the tower.

Openings in the tower - large, arched openings

Virtually all ancient depictions show a large, arched opening in the centre of the first storey. In many depictions that opening is repeated on the other floors. One mosaic (M09) has a black rectangle below the lowest opening, which may be an indication that there was a staircase leading to it. On the Torlonia-relief the opening of the first storey is close to a corner of the lighthouse. It may have been moved by the artist, because most of the tower is covered by a ship, so to make it visible. In the adjacent side is an arched opening with what seems to be a staircase in the interior.

On other depictions only the first storey has a large, arched opening. It could well be that we are dealing with two different sides of the lighthouse, perhaps the side with only one opening turned towards the harbour basin, while the side with many openings was a monumental facade, turned towards the sea, sending a visual message to those who came to Rome.

Openings in the tower - slit windows

Slit windows seem to have been another major characteristic of the tower. They are as a rule in an eccentric position. On one mosaic (nr. M10) they are also in a central position, but that may be a decorative extension of a motif. On one relief (R04) these windows are the only openings, so that this is presumably one of the two sides of the tower. That idea seems to be supported by the scenes flanking the lighthouse: a ship approaching from the left, a tavern to the right. Many modern examples of lighthouses show that there is a relation between this type of window and spiral staircases (of which we have an example in Ostia, in the Round Temple).

Openings in the tower - doors and windows

Most interesting are the two eccentric doors on the second storey of a mosaic on the Square of the Corporations (M03). It looks as if doors in this position can also be seen on the Torlonia relief, on the third and fourth storey. These doors may well have led to spiral staircases. We should then imagine that the staircase was left at the top through a hatch that gave access to the roof of a storey.

We have only a few depictions of windows. On the mosaic with the eccentric doors (M03) we also see two eccentric windows on the third storey. These are hard to understand. Perhaps doors are intended, identical to those on the second storey. Another mosaic (M01) shows doors or windows in the centre of the storeys, flanked by slit windows. This is a very small mosaic, and we may well see the side with arched openings in each storey.

The cylinder

On many depictions flames can be seen that reach far out of the cylinder. The fire guided ships during the night. Pliny the Elder, discussing the lighthouses of Alexandria, Ostia and Ravenna, explains that "the danger lies in the uninterrupted burning of the beacon, in case it should be mistaken for a star, the appearance of the fire from a distance being similar". It is conceivable that the light of the fire was interrupted by a rotating construction. The mosaic with eccentric doors and windows on the Square of the Corporations (M04) shows a bowl-shaped construction below the fire. The fire itself is white on a black rectangle, an unusual way of representing it: on all other mosaics the fire is white on a black background. The fire is flanked by black patches. An attempt may have been made here by the artist to depict a fire that was seen burning with intervals, not easy to do with only two colours and a still image.

The interior of the cylinder must have been made of fireproof material. The tufa blocks of which the ovens of the bakeries in Ostia were made could have been used. On two depictions something can be seen on the exterior of the cylinder (M02) and directly below it (M05): two white dots, and a few short white lines in a rectangle.

The design of the tower and the fuel

The ancient depictions suggest that the lighthouse was quite wide and had many storeys, in contrast to the lighthouse in Alexandria, which had only a few storeys and was relatively slender. As a matter of fact, overviewing the evidence, graffito G03 must be a depiction of the original Pharos. Each upper storey of the lighthouse in Portus seems to have been considerably narrower than the storey below. This is an unusual shape for a tower, and I do not know any parallels. The building looks more like a stepped pyramid than a tower. It should be noted that it is unlikely that the first storey carried the weight of all other, narrower stories. Rather we are looking at several towers, wrapped around each other.

Why did Claudius choose this design? Possibly he wanted his tower to be much different than the original Pharos, emphasizing aemulatio and not just imitatio. It is also possible that he wanted to make the tower sturdier, able to withstand storms, tsunamis and earthquakes. Yet another possiblity is, that this design made the transport of fuel to the top easier. As to the fuel, the Codex Theodianus says that a tax rested on Terracina for "the requirements of the lighthouse and the Port". Another text (Symmachus, Relatio 40,3) informs us that the city provided wood for the baths in Rome and lime for repairing the city walls. Most likely therefore Terracina provided wood also as fuel for the lighthouse. The obvious approach to get it to the top would be to use ropes, pulleys and counter-weights. However, using ropes more than 100 meters long is not practical. The design of the lighthouse in Portus would facilitate the hoisting of the fuel in stages.