The current definition of a Ley-line according to Wikipedia.en.org is as follows:
‘Ley lines are hypothetical alignments of a number of places of geographical interest, such as ancient monuments and megaliths. Their existence was suggested in 1921 by the amateur archaeologist Alfred Watkins, whose book ‘The Old Straight Track’ brought the alignments to the attention of the wider public’.
This explanation by no means completes the modern definition of a ley-line, as we cannot say for example that all alignments of stones are ley-lines, however old they are. Nor does it follow that all ancient sites were aligned deliberately, even those that appear to have been.
Alfred Watkins, the modern founding father on the subject, created the first basic set of guidelines in order to describe ley-lines according to his perception. As we have learned more about ley-lines, so we have had to adapt these original guidelines in order to explain our findings, whilst keeping to the context with Watkins’ original ideas.
The following natural and man-made features were suggested by Watkins to be reliable ley-markers:
Mounds, Long-barrows, Cairns, Cursus, Dolmens, Standing stones, mark-stones, Stone circles, Henges, Water-markers (moats, ponds, springs, fords, wells), Castle, Beacon-hills, Churches, Cross-roads, Notches in hills, Camps (Hill-forts),
Any true Watkinsian ley requires it to have a start (or finish) point in the shape of a hill. (4)
From map and fieldwork, Paul Deveraux concluded that all Henges are likely to indicate the presence of a Ley. (2)
We can therefore begin to gauge the strength of a ley-line according to its length, accuracy of deviation, number of ley-markers and their individual significance.