Secret History
The dozen scratchings were uncovered during a three-week excavation at Nevern in Pembrokeshire.
Archaeologists think the stars and other designs were made by a serf, labourer or soldier some time between 1170 and 1190 when the castle was built.
They say they also give an insight into the beliefs of medieval working men.
Dr Chris Caple of the University of Durham led the archaeological dig at the site and said the slates were from a late 12th century cut-stone entranceway.
"They were found in only one place in the castle and were probably intended to ward off evil," he explained.
"In the late 12th century, Nevern would have been an impressive looking castle and entrance, especially from the south side, and it was clearly visible to all passing along the road between St David's and Cardigan.
The bones were found in El Salto, Durango State, northern Mexico, in a cave hamlet built into a cliff.
The site - called Cueva del Maguey - dates back to around 1425 and was formerly home to the Xiximes tribe.

Bone house: Archaeologists excavate Cueva del Maguey, Mexico, where a cache of human bones was discovered which proves the Xiximes tribe were cannibals
Rumours of cannibalism among the 5,000-strong Xiximes have long existed due to the historical accounts of Jesuit missionaries, which labelled the tribe 'the wildest and most barbarian people of the New World'.

Army of Shadows, 1969 movie about the French Resistance (that never was, apparently)
One of the most persistent wartime images has selfless French men and women in berets and leather jackets blowing up bridges and ambushing columns of German soldiers on lonely country roads.
But a new book by historian Douglas Porch, The French Secret Services, contends almost nothing of the sort actually happened. His account has set the French seething - all the more so since many of them are aware that what he says is absolutely true.
According to the book, even those few French who helped downed airmen often did so for the money. The standard reward for getting an escapee into Spain was about $50,000 in today's money.
Thoai Ngoc Hau (1761-1829), a famous general, helped Nguyen Anh found the Nguyen dynasty (1802-1945). He and his wives were buried in the southern province of An Giang. The excavation of their tombs was carried out on September 19 by local experts. They discovered a number of artifacts buried near the tombs of Chau Thi Te and Truong Thi Met, his first and second wives.
The name on the coin was Minh Duc Thong Bao, minted under the reign of Nguyen Nhac (1788-1793). The discovery in the tomb of the high ranking mandarin's wife has been seen as a possible breakthrough by archaeologists.
According to Pham Huu Cong, it could relate to a secret that had never been made public. "Perhaps the couple had a relationship with the Tay Son movement, the Nguyen kings' foes, and kept the coin as a memento, despite the trouble it could cause. When Chau Thi Te died in 1826, the mandarin buried this coin with her," he said.
Specialists say they have found evidence of at least two Roman forts dating back to the first and second centuries AD.
They would have been used extensively as the Antonine Wall was built.
Archaeologist Martin Cook who is working on the project said the find is one of the most important in the Falkirk area for "decades".
Among the artefacts dug up are bones, jewellery, leather shoes, ceramics, ovens and coins,
The Camelon site, home to the former Wrangler factory, is being cleared to make way for a Tesco store by contractors Barr Construction.
AOC Archaeology, which excavated the land for them, uncovered a rich bounty of archaeological relics.
The medieval burial ground was discovered on farmland in Rush, north Dublin, in June as EirGrid laid piping for a high voltage direct current (HVDC) underground power line.
Radiocarbon tests at Queens University, Belfast, have revealed the site dates back to the seventh century, from between 617 to 675 AD.
Archaeologists would not speculate on the number of remains on the site but confirmed they were pre-Viking and from the conversion period of Christianity.
John Fitzgerald, project director with Eirgrid, said: "It is an interesting historical discovery for the project, local archaeologists and the local community.

Scholars have identified what appears to be the world's earliest Christian inscription, dating to the second century. It is in the collection of the Capitoline Museums in Rome which could not release an image at press time. Also shown, examples of other early Christian inscriptions, copied in 1880.
Researchers have identified what is believed to be the world's earliest surviving Christian inscription, shedding light on an ancient sect that followed the teachings of a second-century philosopher named Valentinus.
Officially called NCE 156, the inscription is written in Greek and is dated to the latter half of the second century, a time when the Roman Empire was at the height of its power.
An inscription is an artifact containing writing that is carved on stone. The only other written Christian remains that survive from that time period are fragments of papyri that quote part of the gospels and are written in ink. Stone inscriptions are more durable than papyri and are easier to display. NCE 156 also doesn't quote the gospels directly, instead its inscription alludes to Christian beliefs.
"If it is in fact a second-century inscription, as I think it probably is, it is about the earliest Christian material object that we possess," study researcher Gregory Snyder, of Davidson College in North Carolina, told LiveScience.
Fossils and Native American tools from eight thousand years ago are easy to find at Lake Whitney, and looters are taking advantage.
They used to be buried in underwater caverns, but the drought has evaporated that protection.
"The looter and scavenger comes and digs up the site," said U.S. Army Corps Engineer Brad Demsey. "They just destroy all that and leave it to the side."
Even in remote parts of Lake Whitney that were once buried under concrete for security, scavengers unearth and discard valuable history.
There are fossils and Native American tools from prehistoric times.
Texas and federal laws ban the removal of Native American artifacts from archaeological sites, but burial grounds have been disturbed.
Research indicates young children expressed themselves in an ancient form of finger-painting. And, just as in modern homes, their early efforts were given pride of place on the living room wall.

Artworks such as this were created 13,000 years ago by children in caves in the Dordogne, research suggests.
Archaeologists at one of the most famous prehistoric decorated caves in France, the complex of caverns at Rouffignac in the Dordogne known as the Cave of a Hundred Mammoths, have discovered that children were actively helped to express themselves through finger fluting - running fingers over soft red clay to produce decorative crisscrossing lines, zig-zags and swirls.
"We have found a prehistoric settlement dating back to 5,000 B.C. But only 5 percent of the settlement exists," said Aslan. The archaeology team examined the coast from the entrance of the Dardanelles to Çanakkale city center, he said. "The coastal excavations had been finished and we unearthed something unexpected around Bozköy."
The settlement was 2,000 years older than Troy, Aslan said. "We know that almost all settlements older than 5,000 years ago were established on high plateaus." The reason for the settlement pattern in high places has been questioned, he said. "This discovery gives us important clues that people settled deliberately because of the rise and fall of the sea," he added.
Aslan said it was the first time that such a settlement was found in the Dardanelles and there is no information about this settlement in any map or document. "We can easily see remains of a 7,000-year-old lost settlement here," he said. "We can call this place a lost city."