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The Almendres Cromlech megalithic complex,near Guadalupe, Évora, Portugal, is one of the earliest public monuments. It is the largest existing group of structured menhirs in the Iberian Peninsula, and one of the largest in Europe.

From wikipedia:
This megalithic monument originally consisted of more than one hundred monoliths[citation needed], some of which have been taken away for other uses. A recent dig showed that the complex had undergone several building phases during the neolithic period (5000 - 4000 B.C.)

It was found rather late, in 1964.
92 menhirs of different sizes currently form two grounds that were built oriented to different equinox directions. Several of them were put back in place

The axis of the ovals is oriented along an east-west direction. The complex's position latitude is about the same as the maximum moon elongation (38.55 degrees for 1500 B.C.); the other latitude at which that happens is that of Stonehenge, 51.18 degrees for 2000 B.C.

About a dozen monoliths present some form of carved drawings, four of which exhibit only small circular holes. Monolith number 8, with a cut flat top at about breast level and showing several dimples, might have served for finer astronomical observation, specially spring equinox observation, by putting small stones on them. These observations might be made from stone 39, on the eastern focal point of the elliptic layout.

It is believed that the monument had religious purposes and functioned as a primitive astronomical observatory.