All over western Europe from Scotland to the Mediterranean are local groups of megalithic
tombs and temples built between the fourth and first millennia BC, numbering several
thousand in all. Orientation was an important consideration almost everywhere, but – just
like other features of design and construction – practices vary from place to place and time to
time. Local orientation practices typically produce sets of
orientations restricted to a limited arc covering at most
one-third of the horizon. This can only be explained by
reference to the diurnal (daily) motions of the skies,
which define the meridian (north–south axis) universally.
A group of distinctive seven-stone “antas” (dolmens)
are found in Portugal and western Spain. Without
exception, every one of 177 measured orientations
falls within the arc of sunrise, providing overwhelming
evidence that they deliberately faced the rising Sun,
perhaps on the day that construction began.