Park somewhere near the large red brick pumping house (you can't miss it) and walk down the narrow lane which runs alongside it. (Don't try to drive down the lane - too narrow). When you come around the other side of the building you will see a path which takes you straight into the cliff fort. This is the only prehistoric site I have been to with a football pitch / goals in the middle of it!! Great views of the Severn Bridge.
[...] Thanks to the members of the corps - about 20 in number - who, under the command of Captain Williams, proceeded to the camp on Saturday last, a sufficient number of tents had been pitched for our accommodation before our arrival en masse on Monday.
[...] There is nothing which indicates the whereabouts of the "soldiery" until one is as it were in the midst of them. The tents are completely hidden from view by the high ramparts which extend from the north-east to the south. The piece of ground enclosed within the ramparts is of a triangular form, the eastern line being formed by the waters of the Severn. Coming suddenly into a deep moat without the ramparts, one is as suddenly confronted by a sentry, marching with a soldier-like air, a guard-room, or rather a guard tent, and a number of the guard lounging about.
Immediately in front of the guard tent, there is a gap, cut right in the angle of the encampment, and looking through this the whole of the tents and their occupants within are at once visible, presenting to the visitor a lively and picturesque scene, of which, two minutes before, he could have had no perception.
[...] The weather has been glorious throughout the week, but the heat, which would be exceedingly oppressive in town, is rendered delightful here, with a stiff fresh breeze flowing across the water. Each day the men have worked and drilled with a subordination that would be creditable even to a soldier of long service, and order has been maintained night and day. Heavy gun drill has been gone into most zealously, and some good practice has been made [...]
Ghost stories are not wanting in the guard room, for one good reason. On the north-east are the ruins of an old Roman chapel known as the chapel of the Holy Trinity, and no doubt was connected with the Roman encampment. Sundry remains of the genus homo in decay have been found in this spot, although the outline of the graveyard which adjoined the chapel has been effaced. A sentry is posted in the vicinity of the old chapel, and more than one have felt a chill creep over him during the still hours; but it is unnecessary to mention the little rumours which have currency during the last couple of days.
I have forgotten to mention that the immediate vicinity of the camp is called Sudbrook, and also that the advantages of the spot were utilised as a place to land, conceal, and protect his soldiers by Oliver Cromwell before he stormed Caldicott Castle. The place is in the highest degree classic and historic ground, and is well worth visiting.[...]
It is almost impossible to realise the extent to which the coast-line must have altered. According to tradition, a long spit of land once ran out from Sudbrook Point in a south-westerly direction, extending as far as the Denny, a rocky islet now lying in mid-channel at a distance of over four miles from Sudbrook.
Sudbrook fort's certainly been nibbled away at by the Severn over the years. And there's a lot of mud about. It's a long way though!
In the 17th C. Camden described the erosion rather elegantly: The Church whereof, called Trinity Chappell, standeth so neare the sea, that the vicinity of so tyrannous a neighbour hath spoiled it of halfe the church-yarde, as it hath done also of an old fortification lying thereby, which was compassed with a triple ditch and three rampiers, as high as an ordinary house, cast in forme of a bowe, the string wherof is the sea-cliffe."
From AE Lawson Lowe's article on the camp in Archaeologia Cambrensis (Jan 1886).
This is taken from Coxe's 1801 'An Historical Tour in Monmouthshire':
To the west of the new passage inn, near the ruins of Sudbrook or Trinity Chapel, are remains of an entrenchment, which are usually supposed to be Roman; they occupy a flat surface on the edge of a perpendicular cliff, and are nearly in the form of a stretched bow, whose cord is the sea coast. The entrenchment is formed by a triple rampart of earth, and two ditches; the two exterior ramparts are low, and in many places destroyed; the interior is in greater preservation, and not less than twenty feet in height [...]
It is generally imagined that this entrenchment, in its present state, is not perfect, and that half of it has been destroyed by the sea, which has likewise carried away part of the church-yard. It is likewise by many supposed to have been a maritime fortress, erected by the Romans to cover the landing of their troops, adn their first station in Siluria; an opinion grounded on the erroneous description [as a square] of Harris, and on the discovery of a single coin struck by the city of Elaia in honour of the Emperor Severus. For notwithstanding repeated enquiries among the farmers and labourers of the vicinity, I could not learn that any coins or Roman antiquities had been found within the memory of the present generation. It has been also attributed to the British, Saxons, and Danes; but was occupied, if not constructed by Harold during his invasion of Gwent.
The ruins of a 12th century chapel lie among the ramparts to the south east, and Coxe mentions "Within the memory of several persons now living, divine service was performed therein; and a labourer whom I met on the spot, assisted forty years ago as pall-bearer, and pointed out the half of a dilapidated grave stone, under which the corpse was interred."