Haverfordwest serves as the market town for most of the county of Pembrokeshire. It forms an important road network hub between other towns in Pembrokeshire such as Milford Haven, Pembroke Dock, Fishguard and St David's, as a result of its position at the tidal limit of the western Cleddau river. The majority of the town, comprising the old parishes of St. Mary, St. Martin and St. Thomas, lies on the right (west) bank of the river. On the left bank are the suburbs of Prendergast and Cartlett. At this point, a pair of sandstone ridges extending east-west and separated by a deep, narrow valley, are cut through by the western Cleddau. This leaves two high spurs on the west side of the river. On the northern spur, the castle and its surrounding settlement form the core of St Martin's parish. On the southern spur, the High Street ascends steeply from the river, and forms the core of St Mary's parish. From the foot of each spur, ancient bridges cross the river to Prendergast: St Martin's Bridge ("the Old Bridge") and St Mary's Bridge ("the New Bridge", built in 1835). St Thomas's parish occupies the south side of the southern spur. From these core areas, the town has spread, mainly along the ridges. In addition to the four ancient parish churches, the remains of an Augustinian priory are visible at the southern edge of the town.
It seems certain that such an obvious strategic location would have been settled in some way from the earliest times. However, there is no documentary or archaeological evidence for the existence of a settlement on the site before the 12th century, when the first Norman architecture castle was established. This occurred around 1110. It was constructed by Tancred, a Flemish marcher lord. The town rapidly grew up, initially around the castle and St Martin's church (the settlement being called Castletown), then spreading into the High Street area. It became immediately the capital of the English colony of Roose (part of Little England beyond Wales), and because of its pivotal position, the commercial centre of western Dyfed, which it has remained to this day. In common with other British towns, its growth was meteoric during the period up to 1300, and its extent by then was much the same as it was in the early 19th century. That being the case, its population was probably around 4-5000 - a large town by the standards of the time. It received its first marcher charter from William Marshall, 1st Earl of Pembroke some time between 1213 and 1219, and obtained the lucrative trading privileges of an English borough. It traded both by land and sea, and had a busy tidal quay on the river below the "New" bridge. At least ten guilds operated, and there was significant woolen cloth manufacture. On 30 April 1479, the town was designated a county corporate by a charter of Edward, Prince of Wales, with the aim of supporting a campaign against piracy in local waters. It shared this distinction only with Carmarthen and a few towns in England, and remained officially "The Town and County of Haverfordwest" until the abolition of the borough in 1974.
In common with other large towns in Europe, Haverfordwest was hit hard by the Black Death in 1348, suffering both depopulation (perhaps by more than 50%) and diminution of trade. Large parts of the town were abandoned, and did not start to recover until the Tudor period. At the end of the 17th century, the town was still significantly smaller than in 1300. In 1405, the town was burned by the French allies of Owain Glyndŵr, although in its early history Haverfordwest suffered less than most towns in Wales from such depredations.
During the Civil War, the burgesses of the borough supported Parliament, while the ruling gentry were Royalist. As a result there was considerable conflict, and the town changed hands five times. There followed a period of stagnation in which the comparative status of the town declined. Haverfordwest today has the air of a typical small country market town, but the centre still conveys the feel of the important medieval borough. The once run-down riverside area has been renovated and Bridge Street has been pedestrianised and improved.
Culturally, the town has always been essentially English in language, but because the town markets traded the goods of Welsh farmers to the north and east, there has always been a significant Welsh-speaking minority, and the air of a "frontier" town. The suburb of Prendergast seems to have originated as an extramural Welsh dormitory, dating from the times when all agricultural trade had to pass through the borough, but no Welshman was allowed within the walls after nightfall.
Dillwyn Miles (ed) A History of Haverfordwest, Gomer, 1999, ISBN 1-85902-738-5,