This article is about the original B4331 from Mathry to Fishguard, in Pembrokeshire.
For the current B4331 from Mathry to Letterston, see B4331
(former B4331) at Panteg
The original route of the B4331 was part of the direct route between Fishguard harbour and St Davids.
It started at the northern end of the A40 in Goodwick, the town next to Fishguard, and headed southwest before ending on the B4330 about a mile east of Mathry.
By 1932 the B4330 had been rerouted east of Mathry and so the B4331 was extended half a mile or so along the former route of that road to reach it at Mathry.
1935 saw even greater changes, as the entire route of the B4331 became part of an extension of the A487 via St David's. It remains this number.