The town of Newport appears to have been carved out of lands that previously formed part of the manor of Stowe, centred on Stow Hill. The earliest known map of Newport, dated circa 1750, shows the borough’s boundaries cutting through existing fields. 
The charter of Humphrey earl of Stafford, 3rd April 1427, gives an account of the medieval boundary and it is still possible to identify it today:
From the graveyard of St Gwynllwg to the native lands of the lord formerly of Robert Houlot and John Dawe, the lands called Brendekyrgh, the croft called Corteyscroft there, and the croft of Margery Watte thereto annexed, the lands formerly of Roger the Clerk called Coumicheshull, thence by the road as far as the chapel of St Thomas so that the entire road there be within the bounds of the town aforesaid, And thence along the road as far as Bryngelond so that the entire road be within the bounds of the aforesaid town, and so along the ditch between the lands and burgages of the Burgesses and the said Bryngelond by descending to the water course of the mill of the lord, and so by the croft of the said Bryngelond and of other lands as far as the fishpond of Kemell, so that the entire water-course there be within the bounds of the aforesaid town, and so by the said fishpond as far as the stone called the Rock opposite the house of John ap Adam, thence beyond the road as far as the lands of the said John and of David ap Ieuan ap David, the lands called the Halys and the meadow called Crinde and so along the river to the Parkpull as far as Groundesende within our lordship and by the land as far as Crokeslonde, Mullond land, Kingshill and the lands of the Abbey of Gloucester as far as the said graveyard. 
From combining this description with the earliest maps of Newport it can be seen that the borough’s original boundary started from the graveyard north of the church of St. Gwynllwg (St Woolos), but with the church itself remaining outside. The boundary ran downhill, north beyond the graveyard (and what is now a small park just to the east of Clifton Place), and then went through a field to the west of what is now North Street, leaving the original Baneswell within the boundary. It continued uphill to the north, crossing the former Mill Street (now Pentonville), and then joined the present Queen’s Hill near the junction with the present Lucas Street. The boundary then ran downhill to join Crindau Pill which it followed as far as the River Usk.
The boundary continued south along the Usk, until it went inland by what is now Usk Way, along the line of a former stream or pill. This pill may be what is referred to in the charter as ‘Parkpull’ (possibly originally ‘Park Pill’), near the later Cross Lane. The boundary reached as far as what was to become the present Commercial Street, and then looped to the south towards the east end of the present Cardiff Road (near the modern Police Headquarters) before it returned north, going uphill back to St Woolos. Bishopstow (referred to by its earlier name of Kingshill in the charter) lay within the boundary of the medieval borough.