Leylines are a most curious phenomena first made famous by an author called Alfred Watkins circa 1928. His book "The Old straight Track" was inspired by a vision he had whilst hiking in the county of Herefordshire in the U.K. where he lived.
The vision he had was of the countryside suddenly becoming interlaced with lines that connected old churches and other places of antiquity. As a result of this split seconds insight Alfred undertook a study of the area using maps and made the discovery that many old churches were indeed connected to each other along perfectly straight lines. Many readers of his work became captivated and sought to undertake similar studies of there own. My own interest having been stimulated led me to make an initial study of my neighborhood. I began my studies using a 1 inch to the mile ordinance survey map. First of all I drew a circle around all the churches that I knew to be (a few) centuries old. Then with a ruler I began checking to see if any of these markers formed straight lines obviously using 3 churches as the minimum criteria. Almost immediately I found many 3 church alignments and a fair number of 4 and 5 church lines. The plot thickened when I extended the lines by some 15 miles or so beyond the last confirmed marker of an alignment. I found that if I extended all the alignments that even though they didn't pass through any more churches - some of these extended lines crossed at exact points on the map. I called these points (Ley crossroads). Using these crossroads themselves as a confirmed marker some of the unconfirmed 2 church leys were now confirmed. It was really a Eureka moment to know that I'd discovered ancient knowledge that absolutely nobody else was aware of. There are other markers that frequently occur on leylines such as pieces of perfectly straight modern roads that follow the route of pre-medieval tracks. Lakes and natural markers such as prominent hills are found often found along the lines. Another more quirky finding is if you regard a church as a central point and draw imaginary circular spiral pattern out from that point - then do a similar exercise with a neighboring church or marker - you may find that the nodes of intersection of the spirals unearth further markers that also form Ley-lines. In addition to markers and geometry, place names are extremely useful as confirmation of a Leys existence. Very old place names such as Cole (Coleshill) or White (Whitecross) etc are examples along with Dodd or Bury and so on. A vital feature to include as a marker in any map search are ancient burial grounds or Earthworks. Alfred Watkins was firmly of the opinion that these tracks were devised as a navigational/ transport network from bygone times. Many students since then have proposed a multitude of other solutions to the riddle. I personally think that sections of the system were perhaps used as roads but am convinced that this was not their primary function. There are many curious folk lore legends attached to the lines as any researcher will soon discover. When I actually visited sites I'd identified, all sorts of confirmations started to appear. Most curious were names of old cottages on the alignments such as Coles Farm or Bury Hill. The most famous Ley-line junction is possibly Stonehenge. What stuck me most about visiting Stonehenge was that it is surround by literally hundreds of earth mounds and other Ley features . From the air the miles surrounding Stonehenge look like a 4000 year old metropolis with the henge itself looking almost insignificant within the mass of features that surround it. The fact that churches contribute so heavily in Ley hunting is a little misleading really. It is not the church itself that's important here it's the land upon which it was built. It became usual with the onset of Christianity to build churches on old pagan sites to lure the enthusiasm of the old ways of the people to the new movement. Upon the old Pagan sites there often stood large standing stones (In fact many church yards still have these relics of Paganism). I think (and many others) believe these monoliths to be key to understanding the Ley-line puzzle. The stones it is thought may have been booster stations forming a network or energy management crossing the entire UK ( &other lands beyond). What type of energy connected the sites is open to much debate. Curiously some stones shows signs of cup marks on their surfaces of various diameters that may have served as satellite type dishes sunken into the surface with their diameters devised to control different frequencies. It is my belief that the energy manipulated by the network was gravity itself. As yet scientist have not been able to detect gravity-waves and I'm sure it's because they simply don't exist. I believe that gravity is a product of distorted space time engineered by the presence of mass. As gravity is a very subtle force it seems feasible to me that the mass of a large stone could be sufficient to cause a local micro-gravitational effects that positioning of the stone and (dish) features upon it's surface could be fashioned in such a way as to harness the (energy/space-time ripple). The mass of Ayres rock in Australia is magnificent example of micro-gravitational anomalous events.
Whatever truth is eventually found to be behind the purpose Ley-lines - it's certainly remains the most captivating of mysteries to solve.