Was just looking through some stuff about the Arthurian legends, and came across something interesting about the Hallows, which are the “royal regalia carried by the King, or the objects sought by someone such as a ‘Grail Quester’”. There’s an interesting section where they compare the 4 hallows of the Tuatha De Danaan, the Tarot suits and the hallowed objects seen in the Grail quest.

Later the Tuatha de Danaan were believed to be a people who were said to have brought sacred treasures from an island near Greece to Ireland from the Otherworld (See Otherworld). There were said to be four treasures:

1. Shining spear of Lugh (from Gorias), providing victory in any fight;
2. Stone of Fal (from Falias), kings were crowned on this;
3. Sword of Nuadu (from Findias), impossible to avoid being struck and wounded by its contact;
4. Cauldron of Dagda (from Murias), of plenty.

The four hallows of the Tuatha de Danaan were developed in later traditions to be:

1. The Pole of Combat;
2. The Sword of Light;
3. The Cauldron of Cure;
4. The Stone of Destiny.

These have since been further developed to the four symbols of magical elements, to also be seen on Tarot packs as the four suits:

1. The Sword;
2. The Spear;
3. The Cup;
4. The Pentacle.

We can see that the sacred vessels influenced the Arthurian legends, Grail legends and the search for the hallowed objects in ancient ‘Annwn’ (See Annwn) also being associated with those of the Tuatha de Danaan:

1. The Sword which is Broken;
2. The Spear of the Dolorous Blow;
3. The Dish (to process the Head of the Withdrawn Grail Guardian);
4. The Grail (Sacred Chalice / Cauldron of Plenty & Inspiration).

Also, I had never heard of Annwn before, the Celtic equivalent of Hades:

aka ‘Annwyfn’. Welsh tradition, said to be the Keltic equivalent to the Hades or the Christian Hell but there is a distinct difference as it is not a place of punishment, or a purgatory, it is an ‘Underworld’ which is ruled by ‘King Arawn’ (See Arawn) where mortals may visit according to the Old Religion.