The B4579 is a hilly road in the region of the England/Wales border. Except for the eastern end, which was part of the A4083, the road was originally unclassified, gaining the B4579 number in 1935.
The road starts at a mini-roundabout on the B4500 in the middle of the village of Glyn Ceiriog and heads east, quickly crossing the Afon Ceiriog and climbing along a narrow road into open country. We follow the river downstream, albeit at some altitude above it, but road and river gradually diverge. There are a couple of detours to cross tributary valleys with little change in gradient and we pass to the south of Bedwlwyn.
Presently, following a descent and some sharp bends, we cross Offa's Dyke, which here is running along the border with England. Another hairpin takes us into Selattyn, after which the road levels out and crosses the undulating fields, becoming S2 as it does so. Presently we reach Oswestry and a T-junction on the B4580.
What happens to the B4579 in Oswestry isn't particularly obvious. Maps differ as to whether the road to the left is the B4579 or the B4580, then various bits of the town-centre one-way loop are given either of these two numbers or else the B5069. Through traffic on the B4579 has to TOTSO left onto Castle Street, then left again at the end onto Beatrice Street. We then go round three sides of Morrisons and double back onto Oswald Road to pass the station. We then turn left onto Black Gate Street to pass Sainsbury's and reach a mini-roundabout, where the B4579 heads left along Salop Road. Traffic heading the other way has an easier route, as Salop Road runs straight into Leg Street and then Beatrice Street, after which we can TOTSO left into Castle Street and then continue as above.
The B4579 originally ended on the A483 in the centre of Oswestry, with the road out of town numbered A4083 until construction of the bypass removed all Class I roads from the town centre. We therefore head southeastwards along Salop Street to pass a retail park and then go over the railway line. After passing an industrial estate the road ends at a roundabout on the eastern bypass, where we meet the A5 and A483.