Many of Ireland's minor roads "may well have had their origin in pre-existing paths and trackways aligned in direct response to the physical environment".
However, a very large oval henge enclosure, thought to date from c. 2500 BC (the Neolithic period) may possibly have had an ancient roadway associated with it.
"[5] An Early Bronze Age trackway, from shortly after 2000 BC, was found at Ballykillen Bog, near Edenderry, County Offaly in the 19th century.
One example from Ballyalbanagh, County Antrim was seven feet (2.1 metres) wide and made from oak beams and planks: "its width suggests provision for cart or wagon transport.
"[11] Generally, most surfaced tracks from this period were made with wood and were designed to facilitate travel through (or to) bogs.
Togher (Irish: tóchar) roads, a type of causeway built through bogs, were found in many areas of the country.
[12] Although law-tracts in Early Medieval Ireland described several different types of road, and Irish annals referred to a network of major highways, there is no evidence to suggest that Ireland ever had a network of roads as well developed as those found in the Roman Empire or other ancient societies.
The development of roads continued throughout the early 19th century until the arrival of the railways which became the dominant form of land transport from the 1840s–1850s onwards.
The night of Conn's birth were discovered five principal roads leading to Teamhair, which were never observed till then.
Slighe Mhór is that called Eiscir Riada, i.e. the division line of Ireland into two parts, between Conn and Eoghan Mór.
Routes tended to follow the line of least resistance, twisting and turning to avoid poorly drained areas and land that was easily overlooked.
Where there was a hill to climb or a difficult area to pass through, multiple tracks would develop, the traveller taking the easiest route.
[16]An early medieval Irish law tract,[17] produced the first written details of different categories of roads that existed in Pre-Christian Pagan Ireland.
A bridge of this type gave Dublin its Irish name: Baile Átha Cliath, 'Town of the Hurdled Ford'.
Because the slightly higher ground of the Esker Riada provided a route through the bogs of the Irish midlands it has, since ancient times, formed a highway joining the east and west of Ireland: its ancient Irish name was An Slighe Mhór meaning 'The Great Highway'.
[22] Roads were not the most important transport routes in later medieval Ireland: most long-distance travel between towns was undertaken by sea or via inland waterways.
Giraldus Cambrensis gives an indication of the slowness of travel in 12th century Ireland, which he also describes as a "truly a desert land [i.e. sparsely populated], without roads, but well watered.
In 1558, it took Thomas Radclyffe, 3rd Earl of Sussex and Lord Deputy of Ireland, two days to travel about sixty miles (c. 100 km) from Limerick to Galway.
[24] In 1614, the Irish Parliament passed the Highways Act which required local parishes to maintain roads within their boundaries which served market towns.
In 1634, a new Act allowed for the levying of a tax "to ensure the repair, maintenance or reconstruction of bridges, fords or causeways."
[1] The difficulties encountered by travellers on 17th-century Irish roads are amply illustrated by extracts from contemporary accounts of journeys.
[27] A military gentleman going from Newry to Downpatrick in 1602 recounts that ...before we had ridden three miles we lost our way and were compelled to go on foot, leading our horses through bogs and marshes...
A few years later an account of the journey of a Scotsman through Ireland in 1619 and 1620 reflects the great difficulties which he encountered: Travelling in winter his horse constantly sank to its girths on the boggy roads, and his saddles and saddlebags were destroyed.
The first butter road was commissioned in 1748 and was built by John Murphy of Castleisland in County Kerry: "one of his routes, opened in 1829, reduced the distance between Cork and Listowel from 102 to 66 miles – quite a feat, given the rough countryside over which it ran.
[36] Several other differences, including in road classification and route-numbering, speed-limits, directional sign-posting and warning and regulatory signposting have developed since the 1920s.
Differing road-numbering systems also mean that some signs in Northern Ireland display route-numbers used in the Republic and vice versa.
The 1925 Act also granted powers to order the removal or alteration of buildings, trees and hedges causing obstruction or danger, introduced a licensing system for the erection of petrol pumps and introduced powers to set speed limits and to regulate signposts.
[45] On 23 July 1969 the Minister for Local Government, Kevin Boland, announced that a national road network would be formed.
The most extensive scheme planned at present is the up-grading of the A5 from Derry to the border at Aughnacoly, County Tyrone from single- to dual-carriageway as part of the A5 Western Transport Corridor.
[86] Work on the motorways continued until the 1970s when the oil crisis and the Troubles both intervened causing the abandonment of many schemes.