Picto-Celtic

A rural world of scattered farms and villages where the typical person is a farmer with the boredom of day to day life broken up by the occasional cattle raid and fey pranks. 

It is also a land where the deep forests, ancient barrow mounds and moonless nights are feared.

The deep forests harbor communities of elves, firbolgs, gnomes, halflings, treants and fey.

Near forgotten stone circles dwell packs of elven were-wolves and unseelie fey.

Skulks and the people under the hills come up from beneath their ancient long barrows to steal cattle on moonless nights.

Raiders live in fortified island villages off the coast. 

These villages are comprised of mongrelfolk fishermen and farmers, half-orc pirates, half-ogre champions and fomorian overlords.

To the west lies a land of warring tribal humans, hill giants, goblinoids, ogres and orcs, just as happy to fight their own kind as each other, the northern part of this land is a mountain chain ruled by frost giants and white dragons.

Further west are mountains dominated by fire giants and red dragons. 

To the east is an archipelago inhabited by a kingdom of bronze dragons and high elves. 

To the south are more civilized areas of human city-states, some ruled by merchant princes and others dominated by snake worshiping theocracies.

PCs can be humans, half-elves or outcasts from the forest or underfolk trying to blend in.

Druids are multi-classed and have at least one level of bard. 

The PCs will fight or unite other tribes, fend off fomorians, explore the forest, barrows, or maybe even the western or eastern lands, perhaps even trade with or raid the advanced southern human merchant/slavers, etc.

Picts - The Pict tribes are a group of peoples loosely tied by similar language, religion and culture. They have no central government and are quite as happy to fight each other as anyone else. They are warriors, living for the glories of battle and plunder, nailing the severed heads of enemies to the doors and wearing them on their belts, warfare is a sport. Clans are bound together very loosely with other clans into tribes, each of which has its own customs. Druids act as priests, political advisers, teachers, healers, and judges. They have their own universities, the right to speak ahead of the king in council, act as ambassadors in time of war and uphold the law. They are the glue keeping together the culture and hold their religious rites in woodland groves, waterfalls, springs and bogs.

Characters 

• Languages:Picts begin play speaking Pict. Those with high Intelligence scores can choose any languages they want (except secret languages, such as Druidic). 

• All classes are illiterate except bards, clerics, druids and wizards.

Permanent Lesser Geas - Every pict starts with at least one lesser geas.

Each tribe has its own, common ones include

never kill a fey (or bard or woman or crow)

never harm a horse (or druid)

never eat mutton (or dog or horse or fish or during a raid)

never drink mead (or during a full moon)

never lie

never refuse a meal, etc, etc, you get the idea.

Characters who get to 10th level must add a Permanent Geas as well.

Classes

Since everyone runs around with just a spear, sword, shield and no armor each class gains 2 more skill points in exchange for each armor proficiency lost.  

example - Fighters get 6 Skill Points per Level (plus Intelligence modifier)

Core Classes - Monks and Paladins are not present among the picts.

Base Classes - only Shifters and Witches.

Alternate Classes - None.

Hybrid Classes - may choose from Hunter, Brawler, Bloodrager and Slayer

Its just a name: Druids are called Apprentice Druids, Mystic Theurges are called Druids

Archetypes

Use some common sense, if it's forest or fey oriented it probably fits right in, if it's a workaround to be a forbidden class then you're a douche.

Prestige Classes

Mystic Theurge, Horizon Walker

Other non-Pathfinder prestige classes that would work in the campaign

Fochlucan Lyrist (Complete Adventurer)

Arcane Hierophant (Races of the Wild)

FEATS

Shield and Spear [Style]

You have learned to use a spear or longspear one-handed while using a shield

Prerequisite: Str 13, Weapon Focus (longspear), proficient with shield, and base attack bonus +4

Benefit: When using this style, if you are using a large shield you can use a longspear one-handed.

Woad Warrior

Prerequisite: Charisma 12+

Benefit: When fighting unarmored and covered in woad you get a +1 to attack or damage, you choose.

Special: This Feat can be taken multiple times, its effects stack and are cumulative.

Religion

For the most part the picts revere nature, rivers, mountains, oceans, lakes, the standard D&D druid religion, plus each tribe also has its own various ancestor demi-gods and gods, two are so common that they have become Intermediate deities. They worship in sacred groves, springs, lakes, waterfalls and bogs, not at the stone circles. The stone circles were built 3,000 years ago by a different culture.

Brigit - chaotic neutral red haired goddess of fire and poetry and also the triple aspect of maiden, mother, and crone. Only females may become one of her clerics.

Domains - Magic and Fire. The third domain varies, it's Charm for maidens, Protection for mothers and Knowledge for grandmothers.

(its charm until the cleric has a child, then its protection until she reaches old age and then its knowledge).

Her clerics are not proficient with armor or shields.

They are proficient with swords, daggers, spear & short-spear.

Once per day can perform a greater turning against undead in place of a regular turning 

(they burst into flame and burn to ash, the undead that is, not the cleric).

Horned God (combination of Arawn and Cernunnos) - antlered pale skinned man who leads the Wild Hunt.

His clerics are lawful neutral and choose from the domains of animal and death

Duties of priesthood: Priests of the Horned God preside over burial and funerals, and must hunt and destroy all undead they encounter or hear about. They can only turn undead and are forbidden to rebuke them. They are likewise

prohibited from casting any spell or use any item that can raise or animate the dead. These forbidden spells include animate dead, create dead, create greater undead, raise dead, reincarnate, and resurrection. Otherwise, priests of the Horned God are the traditional guardians of "mortuary mounds", that is: cold, damp, and foggy places where are buried heroes, rulers, and other important characters. Such places often contain gates that lead to the underworld.

and for those still reading...

History

(4,000 years ago) Wood elves and fey dwell in the forested river valleys and a small population of scattered neolithic human farmers live in small stable communities of rectangular log cabins built on the upland hills and on the coastal plains, avoiding the thickly wooded valley bottoms. They plant wheat and barley, and raise sheep, cattle and pigs and hunt as a supplement to their agriculture. They build communal graves that also serve as centers of religious activity centering on a cult of the dead and fertility. They are driven from the coastal plains by the Fomorians.

(3,000 years ago) Builders - These bronze age folk were farmers, archers, brewers and metal-smiths, they lived in round thatch-roofed houses and built round barrow mounds for their warrior-chieftains and stone circles on the neolithic religious sites for their own gods. They fight off the Fomorians from the coastal plains and slowly drive back the neolithic people who begin hiding in caves under the hills and the wood elves and fey deeper into the forests. 1000 years later after being weakened by a famine and plague, the Fomorians having grown strong again, strike back and kill the rest of the Builders. The famine was brought about by increased cattle stealing in the winter by the people under the hills (as the neolithic folk are now called) and half the wood elves embracing a dark god of vengeance and their clerics cursed with lycanthropy, the elven were-wolves destroyed outlying settlements and small groups of travelers.

(2,100 years ago) The Black Hand - An orc tribe settles in the area and within a few years are decimated by the lycanthropes and Fomorian raiders, a plague finishes the rest. Some of the orc's human slaves survived and formed their own society, worshiping at the great stone circles. 100 years later the descendants of the escaped slaves were forced into serfdom by the high elves.

(2,000 years ago) High Elves - with horses, better weapons and powerful magic drive back the lycanthropes and the Fomorians. They avoid the stone circles and barrows. 500 years later they are defeated by the Pritani.

(1,500 years ago) Pritani - Several iron age tribes who build hill-forts and farms (stone houses with walls around their fields) settle in the area. The Pritani do not pray at the stone circles, in fact they scavenge the smaller stones to build their houses and walls, they do adopt the practice of barrow mounds for their dead though. They are led by a warrior aristocracy that hunt with large war dogs. 1000 years later the last of the high elves have gone away or died, although those with elven blood still exist (half-elves) and their culture merges with that of the Picts.

(500 years ago) Picts - An iron age warrior culture led by druids begin settling in the area.

Randomness

The people under the hills are descendants of bands of humans who were forced to live in the caves and twisting passageways of the underground world. Over generations, these humans adapted to this strange world, filled with natural wonders and dangerous creatures. Some people under the hills have not ventured to the surface in generations, and others have forgotten their true origins altogether.

 However, those who live close to the caves that give entry to the underground realms make occasional forays to the surface and even engage in limited trade with surface dwelling humans.

 The people under the hills are a simple, clannish people dedicated to their homes and the safety of their families. Because of the multitude of evil and predatory races and creatures in the caves and tunnels they call home, people under the hills have become quick, stealthy, and survival-oriented. Although rather primitive and rustic when it comes to technology, people under the hills make up for this lack with a superior knowledge of how to survive beneath ground, although even they avoid the deepest depths of the subterranean realms.

UNDERFOLK RACIAL TRAITS

• Humanoid (human): The people under the hills are humanoid creatures with the human subtype.

• Medium: As Medium creatures, people under the hills have no special bonuses or penalties due to size.

• people under the hills base land speed is 30 feet.

• Darkvision: people under the hills can see in the dark out to 60 feet.

Darkvision is black and white only, but it is otherwise like normal sight, and underfolk can function just fine with no light at all.

• +2 racial bonus on Perception checks: Living as underground hunters for generations has given people under the hills keen senses.

• Camouflage (Ex): Underfolk can change their skin coloration at will to mimic the surrounding terrain, giving them a +4 racial bonus on Stealth checks. In rocky terrain, this bonus increases to +8. This ability works even if viewed with darkvision, although true seeing negates the bonus.

• Light Sensitivity (Ex): people under the hills are dazzled in bright sunlight or within the radius of a daylight spell.

• Automatic Language: Common. Bonus Languages: Drow, Giant, Gnome, Goblin, and Undercommon.

So its a mix of mythology, history and D&D

The high elves are the Tuatha De Dannan from mythology, the builders are the beaker culture from history, the formorians are the vikings.

I want to make an outline of two or three neighboring tribes and was thinking about common geas for the different tribes, like one against drinking mead. And a background story for an elven chainshirt awarded a past human chieftain by local wood elves and the Merrow (aquatic ogre, aka Grendal) that has it in his lair for a starting adventure. Basically along the lines of the PCs are on their first cattle raid and come across a destroyed farmhouse and tracks leading into a mist covered bog.

Each magic item should have a history, like the +1 longsword the party finds after defeating the merrows avenging brothers. It was made by the duergar for a human traitor who led Formians to a sacred wellspring to ambush some druids. Years later, overcome with guilt, he threw it into the well. The +1 dagger was made by a high elf for his daughter long ago and lost when she was mislead by will-o'-wisps and drowned trying to sneak off one night to elope with her human lover etc, etc.

Random bits of unorganized Picto-Celtic information

Each tribe is led by a king, who is subject to an Ard Ri or High King, there are two high kingdoms: one of the north, the other in the south.

Elected Kings lead the tribes and society is divided into three groups: a warrior aristocracy, an intellectual class including druids and bards and everyone else.

Women participate in warfare but not in kingship (maternal grandsons and maternal nephews can be elected king).

One of the most important cultural oddities about the Picts is their system of matrilineal line of succession, descent through the female line, not the male.

After a battle they often dedicate their enemies weapons to the gods and throw them into a river or lake.

Warfare is endemic, society is organized around warfare but this is more of a sport focused on raids and hunting. Tribal conflicts over leadership, land and resources are commonplace, it is more a matter of ritual, than of slaughter, most of the time, this is an age of Hillforts, brochs, crannogs and duns.

The chiefs and the wealthy wear armor taken in battle, bought from other cultures or copied from other cultures.

Though they have a written language, the Ogham script is only used for ceremonial purposes and the picts have an oral tradition. All classes are illiterate except bards, clerics, druids and wizards.

Males are clean-shaven with mustaches, some tribes favor ritualized scarring for the barbarian and fighter warrior elite, some tattoos, some a mix of both.

Copper is used for blue tattoos, ash for black, woad is used for battle wounds and dye.

The intellectual class (bards & druids) use tattoos on their legs to help remember things (+1 to a Knowledge skill check for each tattoo).

Merlin gets to be the leader of the woads cause he is covered with the most dirt and doesn't do anything (King Arthur movie reference).

The ritualistic killing of aging Kings and replacing their Kings who have any infirmities, losing a finger or eye or even going bald, basically any perceived weakness, real or not.

No towns. The basic economy is mixed farming and a few farmsteads around a broch are the norm, cattle raising is more important than cereal cultivation in some rocky, colder regions. Wealth is determined by the number of cattle, horses and followers you have, but gold and silver are good too.

Criminals are killed during a holiday with their guts festively strung in a sacred oak tree, drown in a holy spring or thrown into a bog with their throat cut, each tribe has its own custom.