The Brittenburg, or Lugdunum Batavorum, is a Roman ruin west of Leiden that was visible on the beach between Katwijk aan Zee and Noordwijk aan Zee after storms in the years of 1520, 1552 and 1562. It was quite a large complex located at the mouth of the Oude Rijn (old river Rhine), which today is believed to be about a kilometer westwards (offshore in the North Sea) of the current location of the European Space Research and Technology Centre.
The site, known as "Brittenburg", was still visible in the dunes in the fourteenth century, but the gradual advance of the sea made the ruins lie on the beach in the sixteenth and seventeenth century. Today, they must be somewhere in the Rhine estuary, inaccessible for archaeological research. All that remains is a small set of finds, taken away in the sixteenth and seventeenth century, and a famous map by Ortelius. A copy of the old Roman map Tabula Peutingeriana shows Brittenburg as Lugduno on the coast with two towers. Eastwards from that point, two roads run towards Noviomagi (Nijmegen). Along the northern route, the following towns can be seen: Pretorium Agrippine (Valkenburg (South Holland)), Matilone (Leiden), Albanianis (Alphen aan den Rijn), Nigropullo (Zwammerdam), and Lauri (Woerden). All of these locations are situated on the Oude Rijn. The southern route begins with the town Forum Hadriani (Voorburg), shown directly south of Matilone. These towns were connected by the Fossa Corbulonis or Corbulo-canal.
The first mention of the Brittenburg in a Dutch text is in a poem of Willem van Hildegaersberch in 1401, who called it Borch te Bretten. In 1490 there is also a mention of the visibility of the "burg te Britten". The 'discovery' was in 1520 when a storm exposed the whole complex and Roman artefacts (mainly stones and coins), were found. Some coins were dated, with the latest date being 270. The oldest picture of the Brittenburg is a woodcut (identified by Leiden professor Jan Hendrik Holwerda, curator of the Rijksmuseum van Oudheden) by Abraham Ortelius in 1562 for Lodovico Guicciardini's first edition of The Low Countreys, printed in 1589 by Christophe Plantin in Antwerp. This woodcut was replaced in later editions with an engraving. The oldest picture was used later by Zacharias Heyns (1598, 1599) and Hermann Moll (1734, 1736). It concerns a land surveyor's draft (trigonometry), in which the distance from the ruins (by that time in the North Sea and only visible at low tide) westward to the church of Katwijk is mentioned, namely 1,200 'schreden' (= 1,080 meters).
Brittenburg was part of the Roman border defense (limes), as the guard post (castellum) called Lugduno, the western-most position situated the along the Old Rhine, which formed the northern frontier of the Roman province Germania Inferior. Given the square shape of the inner structure, the Brittenburg was probably a lighthouse after the model of the lighthouse of Ostia Antica with a height of about 60 meters and a basis of 72 x 72 meters. Some historians see in the plan also a granary, but for this a dryer, more inland location would have made more sense.
Burcht te Bretten 
There has been a lot of confusion about the terms Brittenburg and Lugdunum Batavorum. The mysterious 'burcht te Bretten', a castle situated supposedly somewhere around Leiden (Bretten is the oldest name for the area between Leiden and the North Sea), has been sought since the Middle Ages. When the remains at Katwijk were rediscovered in 1520, they were (incorrectly) called Brittenburg for this reason. There were many burchts in this area that fell into disuse and were later torn down to reuse the stones in construction.
Burcht van Leiden 
When the Tabula Peutingeriana was discovered by Conrad Celtes around 1500, Leiden scholars assumed that an old shell keep in the city center called the Burcht van Leiden, at the spot where the Leidse Rijn met the Oude Rijn, was Lugduno. Leiden has called itself (incorrectly) Lugdunum Batavorum for this reason. The Latin name of Leiden University is Academia Lugduno Batava. The Batava was only added to distinguish Leiden from another Lugdunums. This term is even more unfortunately chosen, since those same scholars also assumed that Leiden was located within the old Batavia (region), which was in fact much further east, near Germany. Lugdunum was in the territory of the Cananefates, not the Batavi. Today Leiden is associated with the town Matilone on the tabula, and even that spot is considered to be a location somewhat eastwards of the Burcht van Leiden, at the site of a former cloister called Roomburg.
Tower of Kalla 
The Roman historian Gaius Suetonius Tranquillus wrote a story about the emperor Caligula, who lined up his soldiers and artillery on the beach and declared war on Neptune, god of the sea. After that he claimed victory over the ocean and commanded his men to collect shells as war booty. As a monument to this victory he built a tall lighthouse. This story resulted in a search for Caligula's lighthouse. In the 16th century, when many early tourists came to see the Brittenburg at low tide, people from Katwijk reported that their fishing nets were regularly stuck behind the stones of what they called "Kalla's tower" (Kalla = Caligula). This story of Caligula is probable, because a wine barrel was found originating from his personal vineyard in this area.
Considered to be part of Lugdunum, the Roman army supply base Praetorium Agrippinae, modern Valkenburg, is said to have been founded by Caligula. Modern archeologists have found traces of Roman infrastructure and have installed ways to see these in the modern landscape.
New Brittenburg 
South east of the Brittenburg is now the sole reminder of the ancient structure: the bus stop Nieuw Brittenburg (New Brittenburg), the main bus stop for the city centre and the beach of Katwijk.
- D. Parleviet, "De Brittenburg voorgoed verloren", Westerheem 51.3 (2002).
- Suetonius, Life of Caligula 46
- Simon Wynia, "Gaius Was Here: The Emperor Gaius' Preparations for the Invasion of Britannia: New Evidence", in H. Sarfatij, W. J. H. Verwers, and P. J. Woltering, ed., In Discussion with the Past: Archaeological Studies presented to W. A. van Es (Amersfoort, 1999).
- Brittenburg, raadsels rond een verdronken ruïne, H. Dijkstra and F.C.J. Ketelaar, Fibulareeks 2, Uitg. C.A.J. van Dishoeck, Bussum, 1975.
- De Brittenburg voorgoed verloren, D. Parleviet, in Westerheem 51/3, 2002.
- The Brittenburg on the site of Digitaal Erfgoed Nederland
- Illustration of The Brittenburg in family archive Van Wassenaer Van Duvenvoorde