The broken menhir was erected around 4700 BC, at the same time as another 18 blocks nearby, it is thought to have been broken around 4000 BC. Measuring 20.60 metres (67.6 ft), with a weight of 330 tonnes, the stone is from a rocky outcrop located several kilometres away from Locmariaquer. The impressive dimensions of this menhir still divide specialists about the techniques used for transport and erection, but the fact that this was achieved during the Neolithic era remains remarkable.
Worked over its entire surface, the monument bears a sculpture representing a « hatchet-plough ». Unfortunately today this is seriously eroded and very difficult to see.
It is not known what caused the menhir to topple and break into the four pieces that are now seen. At one time it was believed that the stone had never stood upright, but archaeological findings have proven that it did. The most popular theory is that the stone was deliberately pulled down and broken. Certainly other menhirs that accompanied it were removed and reused in the construction of tombs and dolmens nearby. However, in recent years, some archaeologists have favoured the explanation of an earthquake or tremor, and this theory is supported by a computer model.
Source : Wikipedia.