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The ziggurat of which we are writing in this paper is the Ziggurat of Ur. This structure was a huge building in a large complex dedicated to the worship of the Moon-God patron of Ur. This monument seems having a specific alignment along to the northern possible direction of moonrise.
A Ziggurat and the Moon
Amelia Carolina Sparavigna, Politecnico di Torino
Abstract: The ziggurat of which we are writing in this paper is the Ziggurat of Ur. This structure was a huge building in a large complex dedicated to the worship of the Moon-God patron of Ur. This monument seems having a specific alignment along to the northern possible direction of moonrise.
The Ziggurat of Ur was built in the 21st century BC in the city of Ur near Nasiriyah (Figure 1). It was a structure of the Early Bronze Age, that was restored in the 6th century BC by King Nabonidus. In modern time, the remains of this ziggurat were discovered by William Kennett Loftus in 1850. In the 1980s, under Saddam Hussein, the remains of Nabonidus ziggurat were subjected to a partial reconstruction of the facade and of the monumental staircase . The step pyramid measured 64 m in length, 45 m in width. Speculative 30 m in height are supposed, because only the foundations of the ziggurat have survived . Besides this structure in Ur, another well-preserved ziggurat is that of Dur Untash (Chogha Zanbil) .
As we can find in , the ziggurat was built by King Ur-Nammu who dedicated it in honor of Nanna/Sin, the moon-god, during the Third Dynasty of Ur. The ziggurat was one of the buildings of a large complex that was also the administrative center for Ur and a shrine of the moon-god, patron of the town . As previously told, the first restoration of the ruined tower was due to King Nabonidus, who, after "finding little left but the last stage and nothing to guide him as to the monument's original appearance", restored in seven stages rather than three .
As previously told, the remains of the Nabonidus ziggurat were first discovered by William Kennett Loftus in 1850 . The first excavations at the site were conducted by John George Taylor in the 1850s, who identified the site as Ur . After World War I, some preliminary excavations were made by Reginald Campbell Thompson and Henry Hall. Then the site was extensively excavated by Leonard Woolley, for the University of Pennsylvania and the British Museum in the period of 1922 to 1934. Today, we see a ziggurat of which the lowest layer corresponds to the original construction of Ur-Nammu, while the upper layers are part of the Neo-Babylonian restorations .
The precursors of the ziggurat were raised platforms, that were built during the fourth millennium BC . In their final form, they were pyramidal structures with a flat top, with a core made up of sun-baked bricks, covered by fired bricks. "The facings were often glazed in different colors and may have had astrological significance" . Archaeologist Harriet Crawford tells that it "is usually assumed that the ziggurats supported a shrine, though the only evidence for this comes from Herodotus, and physical evidence is nonexistent. It has also been suggested by a number of scholars that this shrine was the scene of the sacred marriage, the central rite of the great new year festival " .
As stressed in , the ziggurats were not places for public worship or ceremonies, because they were "dwelling places for the gods and each city had its own patron god". In the case of Ur, the god was Sin or Nanna, the god of the moon in the Mesopotamian mythology of Akkad, Assyria and Babylonia (note that the moon deity was a god, not a goddess). As a Sumerian deity, he was Nanna the son of Enlil and Ninlil, that, from the Akkadian Empire period, was identified with Semitic Sin . The two main seats of Nanna/Sin worship were Ur in the south and Harran in the north of Mesopotamia.
During the period that Ur exercised its supremacy over the Euphrates valley, the Moon-God became the head of the local pantheon , so he was designated as "father of the gods", "creator of all things", and so on. He was also the "wisdom" personified, imagined as "an expression of the science of astronomy or of the practice of astrology, in which the observation of the moon's phases is an important factor" .
In fact, in the astronomical knowledge, the people of Mesopotamia surpassed the other ancient civilizations, even the Egyptians . "They confined their observations to the Moon, instead of the Sun. … They had built observatories, or watch-towers, called Ziggurats. The tower of Babel is the best known example" . From these towers the priests/astronomers had the possibility to observe the rising and setting of moon, sun, planets and starts on a free horizon. They recorded data and had tables from which they were able to predict the positions of celestial bodies . So we have the lunar observations reported in clay tablets, inscribed "with cuneiform writing recording the times and dates of moonrises and moonsets, the stars that the Moon passed close by, and the time differences between rising and setting of both the Sun and the Moon around the time of the full moon". In this manner, the Babylonian astronomy discovered the main periods of the Moon's motion and used data analysis to build lunar calendars based on the Metonic cycle [8-10]. It is possible therefore, that in the shrine on the top of ziggurats, not only the solar new year had been celebrated, but also the great Metonic cycle of a lunisolar calendar.
In  it is told that "the Babylonians seem to have lacked any geometrical or physical interpretation of their data, and they could not predict future lunar eclipses". However, Mesopotamia had geometry for sure, necessary to build such structures. And a simple geometry was probably used to connected the motion of the sky and of the moon to the orientation of their ziggurats. For instance, in the Figure 2 we can see that the Ziggurat of Ur is aligned along the moonrise azimuth on a lunar major standstill (for the detailed description of lunar standstill, see please ). Probably, this alignment of the staircase and side of the temple along the northern possible moonrise azimuth is not a mere coincidence (however, let us note that such precise alignment could be due to the modern restoration of the ziggurat). The panels of Figure 2 had been obtained using the Photographer's Ephemeris software, where the blue lines are giving moonrise and moonset azimuths, whereas the yellow and orange lines the sunrise and sunset direction. The date of simulation is April/May 2025, when a major lunar standstill will be.
Let us conclude showing also the image of Dur Untash (Chogha Zanbil). The diagonals of this tower are less than a degree different from the cardinal directions (Figure 3). The ziggurat is dedicated to Inshushinak, one of the major gods of the Elamites and the patron of Susa. The remarkable alignment along the cardinal directions seems stressing the fact that these platforms were used for astronomical observations and that the worship of gods was strictly linked to the sky.
Figure 1: Ur in a Google Earth image
Figure 2: The northern moonrise azimuth happens on a major lunar standstill. Here in two panels we can see a simulation, for the major standstill of April/May 2025, obtained by means of the Photographer's Ephemeris. The pale blue line is representing the moonrise azimuth, the dark blue the moonset. Note the alignment of the structure. Yellow and orange lines are the sunrise and sunset azimuths. Simulations with this modern Ephemeris had been used in some previous papers to see the orientation of towns and buildings with respect to moonrise [12-15].
Figure 3: The satellite image of Google Earth is showing the Dur Untash (Chogha Zanbil) ziggurat. The diagonals of this tower are less than a degree different from the cardinal directions.
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1 added 18th June, 2016 at 16:26:28
On a major standstill, the moonrise azimuth at the Ur latitude is about 56 degrees (true north); on a minor standstill, the azimuth is of 69 degrees. The difference is then of 13 degrees. It seems a small difference. However, we have to consider that the angular diameter of the moon is half a degree. It means that, on the horizon, the difference corresponds to 26 moons, which is clearly a relevant quantity.