A detailed description of the castle is given by Jeremy Knight in The Monmouthshire Antiquary (1991). The castle surviving today consists of the east range which faced the river. Originally there would have been a curtain wall, roughly rectangular in plan, running behind the east range. There would also have been a surrounding moat with presumably drawbridges for entrances that were on the north and south sides. The surviving stone castle was greatly altered in the 20th century.
The east range consists of three towers linked by straight walls, the main hall, a water gate, a vaulted audience chamber, and a kitchen block. The north tower has two stories on a solid square base, and is thought to have been the quarters of the constable or steward of the castle. This tower was attached to the hall which stood at first floor level over a vaulted cellar or undercroft. There was a chamber between the hall and the central tower, with a spiral staircase attached to the corner of the tower.
The central tower is the largest tower. It contained an impressive vaulted chamber over a water-gate allowing ships direct access to the castle. Above the vaulted chamber there may have once been a chapel. To the south of the central tower was a smaller room, probably the withdrawing room for the lord, as a gallery then leads to the south tower, which is where the lord of Newport would have stayed on his visits to Newport. The kitchens are thought to have been behind the gallery.
The castle was the administrative centre for the lordship of Newport and in its heyday it would have dominated the town and the river crossing. However there is uncertainty about when the earliest castle in the borough was built, and whether this earlier castle was on the same site as the present castle.
Knight’s view was that the date of the foundation of the present stone –built castle must lie in the bracket 1327-1386. However a recent survey by Cadw suggests there were a series of building periods, dating back to the Clare lordship in the thirteenth century.  Knight would have been unaware that the north curtain wall may have been earlier in date than the rest of the castle.
A Norman motte on Stow Hill is discussed elsewhere, but what is in question is whether there was once another castle, predating the thirteenth century, somewhere near the present castle. It is recorded in the Welsh Brut Y Tywysogion that in about 1172 AD King Henry II visited Castell Newyd ar Uysc (New Castle on the River Usk). In 1185 the king’s accounts show that six pounds fourteen shillings and sixpence were spent on repairs to the castle of Novi Burgi (i.e. Newport) and its buildings and bridge. This does not sound like the motte on Stow Hill, which was outside the borough’s boundaries away from the river and with no view of medieval Newport - since it faced towards the Severn Estuary and the mouth of the River Usk. Further it is unclear how the bridge or town could have been properly defended if there was no castle close to it.
There are various references in the thirteenth and fourteenth centuries to Newport Castle and town, including details of a siege in 1321 by Hugh Audley and other lords. The damage was so bad that in 1322 an order was given for 300 oaks ‘fit for timber’ to be felled to repair and construct the houses and fortalices (outworks) within the castle.  This would seem to suggest that at this time the castle may have been constructed of timber, but the reference does not specifically refer to the main castle itself, where presumably the structure survived the assault.
The oldest plan of the castle and its original curtain wall is shown on the town map of 1750. ( click
here to view ) The moat is not shown and the main buildings on the riverfront are shown out of the correct alignment. A plan for William Coxe’s An Historical Tour in Monmouthshire in 1801 appears to have been based on this earlier plan since it shows the same mistake regarding the building range, but it does show a moat. ( click
here to view ) In 1885 Octavius Morgan published a surveyed plan ( click
here to view ) of what then existed in Archaeologia Cambrensis, and up to date plans were published by Jeremy Knight in 1991.
The archaeological evidence largely consists of a coin of Edward III excavated in 1845,  and some roofing slate and some fifteenth or sixteenth century pottery excavated in 1970. Architecturally the surviving castle does not appear to be any earlier than the thirteenth century, but it is clear that the present castle is the partly the same castle that was severely damaged by Owain Glyndŵr in 1403. Possibly a fourteenth century stone castle replaced an earlier castle in the same vicinity.
Other documentary evidence to the surrounds of the castle include a building called ‘the long stables’ outside the castle gate in 1452, the rabbit warren in 1484, and various references to the castle green which appears to have been on the north, west and south side of the curtain walls. By the end of the fifteenth century the castle appears to have been neglected and a survey of 1522 refers to ‘a fair hall, proper lodgings after the waterside, and many houses of offices; howbeit, in manner, all is decayed in coverings and floors, especially of timber work.’ The later history of the castle is outside the scope of this survey.
1. Forthcoming report for Cadw by Will Davies, Christopher Phillpotts and Bob Trett
2. Calendar of Close Rolls 15 Edward II Volume 1318-1323. 440
3. Monmouth Merlin and South Wales Advertiser 27 September 1845. The report also refers to coins ‘of the Henries and several base coins of the age of Constantine, but too corroded to decipher’. What the significance is of the Roman coins is impossible to say without any further archaeological evidence.
Bob Trett 2010
Newport Castle Chronological Chart and