Bosham Harbour (Magnus Portus)


The natural harbours between Portsmouth and Chichester, have been known as Magnus Portus or “the Great Harbour” from the writings of Ptolemy. Roman remains are have been discovered over the years.  They found a Roman foundation under Trinity Church.  In 1800, a colossal head (much eroded) was discovered in a garden; it is thought to have belonged to Emperor Trajan’s statue sited at the entrance to the harbor.  Excavations uncovered pottery, midden pits, even wallplaster and opus signinum (Roman waterproof mortar). In the 19th century a roman footbath was discovered in Bull’s Garden, next to Bosham churchyard.  In 1832 near Broadbridge house, they discovered the foundations of a building, with walls over 2 feet thick and 6 feet deep with a 6 foot circular bath, an atrium and other rooms, thought to have been used by the troops.  Antoninus coins were found embedded in the tile mortar.  It is said that archaeologists found the remnants of an ampitheatre, and also a Roman mill-race. There is no Latin inscription on stone recorded in the R.I.B. for the Bosham Harbour site.

A legionary helmet which was dredged-up from Bosham harbour many years ago. This helmet has been described as a ‘Jockey Cap’ type, which was phased-out of service with the Roman army in late-Claudian times, in favour of an improved design with better neck and cheek protection. This helmet now resides in the Lewes Museum. Helmets similar to that at Lewes are a sure sign of Claudian military activity.” (Dudley & Webster, p.201, #22)

Was Bosham an Invasion site for Claudius?

It has been claimed by some that the known Roman harbour at Bosham, which is naturally split into three major tributaries, was the original landing site of the Roman invasion of 43AD, but this cannot be reconciled for a number of reasons. For a start, the Romans were very averse to sea-borne operations of any kind, especially on their north-western seaboard which was subject to that very un-Mediterranean problem of tidal currents, and they would have been very wary of extending their initial supply-lines this far along the southern coast. Secondly, dio mentions a two day long battle at a major British river before the Thames, and there is no likely candidate between Chichester and London.

Bosham Harbour and the nearby legionary depot at Chichester may be assigned to the secondary thrust of the invasion period, probably early in 44, when the Second Legion Augusta commanded by the future emperor Vespasian saw active service against the Durotriges and the Belgae tribes in southern England. This conflict is touched upon in Suetonius (Vespasian IV.1).

Historical References to Bosham Harbour (Magnus Portus)

Geography of Ptolemy published in the early-second century AD, provides us with a fairly accurate picture of The Island of Britain at the time. In book II chapter ii, Ptolemy describes the coastal outline of Britain, giving the latitude and longitude of a number of promontories, river-mouths, peninsulas and bays, and his paragraph headed “the description of the south side below which is the Oceanus Britannicus”, gives the names of several features on the southern English coast. Here, between the rivers Iscas and Alaunus to the west and the Trisantonis¹ to the east is a place known as Magnus Portus or “the Great Harbour”, which must refer to the natural harbours between Portsmouth and Chichester.

  1. The Iscas is certainly the River Exe in Devon, the Alaunus is yet to be identified but probably flows through the county of Dorset, and the Trisantonis has been equated with the River Arun in Sussex.

The Bosham Legionary Helmet


References for Magnus Portus – The Great Harbour

The Roman Conquest of Britain by Graham Webster & Donald R. Dudley (Batsford, London, 1965).

Sites near Bosham Harbour (Magnus Portus)