Star.pngStar.pngStar.pngStar grey.pngStar grey.png


From Roader's Digest: The SABRE Wiki
Jump to navigation Jump to search
Location Map ( geo)
Cameraicon.png View gallery (17)
From:  Ponterwyd (SN749808)
To:  Llanbadarn Fawr (SN599808)
Via:  Devil's Bridge (Pont ar Fynach)
Distance:  14.7 miles (23.7 km)
Meets:  A44, B4343, B4574, B4340, A487
Former Number(s):  B4344, B4581
Primary Destinations
Highway Authorities


Traditional Counties


Route outline (key)
A4120 Ponterwyd – Devil's Bridge – Llanbadarn Fawr


The A4120 is a fantastic road that I remember from childhood holidays to Devil's Bridge.

We start on the A44 at Ponterwyd, although if you have come up from Rhayader, you are just as well to cut the corner off on the B4343. Almost immediately, we cross a bridge over what I remember as a wide river, but it looks like just a little stream on the maps! Soon Ponterwyd is behind us, and the road meanders through fields with several sharp bends, each with a layby on the outside. Is this evidence that they were once even sharper?

The B4343 then drops steeply and sharply down from the left, with a rather terrifying link if you wish to turn left onto it - unlikely. We are now travelling southwards with a steep hill on our left, and pass through Ysbyty Cynfyn, where a small chapel marks the site of a monastic hospital. Apart from a couple of caravan sites, nothing else much happens until we reach Pont-ar-Fynach, where the Devil's Bridge (see below) crosses the Monks River (Afon Mynach).

Immediately around the corner from the bridge the B4574 hairpins back to the left, and then we pass the impressive hotel, before the road winds round through the village, passing the terminus of the narrow gauge Vale of Rheidol Railway. Next left is the continuation of the B4343, which therefore must have been multiplexing with us for some time! Soon after, the village is left behind and the A4120 becomes a real country road, linking the small villages that sit on this open hillside far above the steep-sided Cwm Rheidol.


Roads turn off to the left climbing into the hills, and to the right they drop steeply down through the trees to the valley floor. But the A4120 soldiers on, with sharp bends and steep hills taken in its stride. You just about get the feeling that all of the bends are to hug the contours when a steep climb or sudden drop emerges, and yet even then it's not straight. Capel Seion and Moriah are passed, before the outskirts of Aberystwyth finally appear in the distance. The road is now dropping downhill to meet first the B4340 and then the A487, which both run southwards, parallel to each other for about 1/4 mile before they diverge!

But that is not the end! The A4120 used to cannon off the A487 and head north towards the A44. Now, after a short northbound multiplex, we turn off right at a new roundabout and drop down a hill that is not as steep as it used to be to pick up the old route and follow Heol y Bont across the River Rheidol and two railway lines (Vale of Rheidol and Aberystwyth to Shrewsbury) at separate level-crossings to the A44. Halfway along a large roundabout gives access to the retail parks and Boulevard Saint Brieuc / Park Avenue which leads to the Town Centre. When this road was first opened, some maps showed it as a rerouted A487, with the A44 diverted down the other piece of the A4120 to meet it at this roundabout, but that appears to have just been wishful thinking!

The Devil's Bridge

The Devil's Bridge

The Bridge in Pont-ar-Fynach is an interesting structure, comprising three bridges spanning the falls of the Afon Mynach as it drops into the Afon Rheidol. The lowest is a twelfth century stone arch bridge, spanned by a 18th century bridge higher up, and then the 20th century metal deck above them all. From below, it is clear that the original bridge was not really that useful, as it would have needed a very steep descent and climb to use it.


The majority of the A4120 was originally the B4344, however it was quickly upgraded to Class I status, and was given the A4120 number in the mid-1920s. The western end of this road was on the A487 at Penparcau. The road north to Llanbadarn Fawr was originally unclassified and became the B4581 in 1935 but then did not become the A4120 until at least the 1960s.

Related Pictures
View gallery (17)
The A4120, after the snows - Geograph - 1665410.jpgThe A4120 thaws out in Pisgah - Geograph - 1658549.jpgLevel crossing - times two - in... (C) Eirian Evans - Geograph - 2106487.jpgVale of Rheidol Railway (C) John Lucas - Geograph - 659211.jpgLevel crossings on A4120 (C) John Firth - Geograph - 3558246.jpg
Other nearby roads
A4100 • A4101 • A4102(W) • A4102(E) • A4103 • A4104 • A4105 • A4106 • A4107 • A4108 • A4109 • A4110 • A4111 • A4112 • A4113 • A4114 • A4115 • A4116 • A4117 • A4118 • A4119
A4120 • A4121 • A4122 • A4123 • A4124 • A4125 • A4126 • A4127 • A4128 • A4129 • A4130 • A4131 • A4132 • A4133 • A4134 • A4135 • A4136 • A4137 • A4138 • A4139
A4140 • A4141 • A4142 • A4143 • A4144 • A4145 • A4146 • A4147 • A4148 • A4149 • A4150 • A4151 • A4152 • A4153 • A4154 • A4155 • A4156 • A4157 • A4158 • A4159
A4160 • A4161 • A4162 • A4163 • A4164 • A4165 • A4166 • A4167 • A4168 • A4169 • A4170 • A4171 • A4172 • A4173 • A4174 • A4175 • A4176 • A4177 • A4178 • A4179
A4180 • A4181 • A4182 • A4183 • A4184 • A4185 • A4186 • A4187 • A4188 • A4189 • A4190 • A4191 • A4192 • A4193 • A4194 • A4195 • A4196 • A4197 • A4198 • A4199
Former iterations: A4105(W) • A4105(E) • A4108 • A4114 • A4115 • A4116 • A4125 • A4141 • A4150 • A4154 • A4160 • A4168

SABRE - The Society for All British and Irish Road Enthusiasts
Discuss - Digest - Discover - Help