Indiana Jones and the Grail Tablet
The grail tablet was one of two markers left by three brother knights of the first crusade. The third night who was dying of extreme old age tells his story to a Franciscan friar, that he, along with his two brothers, Richard and the Grail Knight had set out to find and protect the Holy Grail of Jesus Christ. Which they did in the temple of the sun in the canyon of the Cresent moon in Halay. 150 years after finding the grail two brothers started their journey back to France leaving the grail knight to guard the relic. The grail tablet was one of the markers left by one of the two returning brothers. The other was Sir Richards's shield buried with him in the catacombs of Venice. Both markers were there to describe the location of the Holy Grail. The tablet was made of sandstone, made in the Middle East, and was found by Walter Donovan's people who digging out there for copper in the mountains north of Ankara, I believe.x
Indiana Jones and the Cross of Coronado
The Cross of Coronado is an artifact that only appears in the first scenes of the 1989 George Lucas-produced and Steven Spielberg-directed blockbuster.
Far more importantly, the cross helps establish the mindsets of Father and Son in the early days and how their stories or motivations have changed over the next 30 years.
Indiana, an altruistic teen, looking out for the public good, believes that historical artifacts should be shared with the world and not in the hands of private collectors. Indy later turns mercenary. So, by 1935, we find Jones willing to sell the ashes of Emperor Nurhaci to crime boss Lao Che for diamonds, eventually moving closer to wanting more than material objects to something somewhat spiritual, as he does in Raiders of the Lost Ark.
It also shows how the Jones' succumb to their obsessions and tend to lose themselves to them.