The Shields of Mikhail
Fortress Dwarves of the Twin Cities
The Fortress Dwarves are skilled miners, warriors and builders of grand fortress cities. They mine precious metals and trade it and other materials with the other races. They hole up in their cities in times of danger but have been known to unite under a single banner to combat a larger threat.
Short and Stout
The Fortress dwarves are shorter than humans, generally being under 5 feet tall but their larger stature means that they can easily weight more than one. Their skin ranges from deep, reddish or tan shades of browns of the dwarves of Vikfjell to the paler shades of grey of the dwarves of Dahlborg Their hair is usually brown, gray or black which is tied up behind the head or kept short. The males can grow magnificient beards but prefer them short or shaved.
Fortress Dwarves prefer colourful and expensive clothes, the brighter and fancier the clothes, the wealthier the Dwarf. Some dwarves that have completed their Combat Training like to wear a part of their armor with their daily wear as proof that they have completed their duty.
The Life Inside a Fortress
The Fortress Dwarves mature at the same rate as humans, but can live to be over 200 years old. They love their ancient traditions and mannerisms and have a tight code of honourisms and titles that can only be dropped by the closest of friends. These can be difficult to understand for outsiders and failure to follow them can lead to distrust and lack of trade between communities of Fortress Dwarves and others, but if you understand the traditions and befriend a Fortress Dward, they will probably be the most loyal friend you can ever have.
When a Fortress Dwarf comes of age at his twentieth birthday, they have the option of going through the Combat Training which can take up to three years. The standing militia of Dwarven Fortress cities consists mainly of younger dwarves going through their training and older, veteran dwarves who have been hired by the city to defend it and keep order. After a Dwarf has completed the Combat Training, he can keep the equipment that has been assinged to him. A Dwarf can decline to take part in the Combat Training, but most see it as a duty and Dwarves who have seen battle as part of the militia are glorified and the ones who skip it are seen as cowards.
The Hatred of Millenia
A long, long time ago, the Fortress Dwarves were divided by a feud between the two oldest clans of the city of Dahlborg; Clan Brandson led by Brandr Brandson, the Fifth of His Name and Clan Agnarson led by Agnar Agnarson, the Fourth of His Name. The feud was long and violent and ultimately led to Agnar taking his clan and his allies and building the Fortress City of Vikfjell near the Boiling Bay and began directly competing in with Dahlborg. To this day the Dwarves if Vikfjell and Dahlborg hate each other with a passion and a Fortress Dwarf finding himself in the "wrong" city is bound for a bad time.
The Greed for Gold
Most Dwarves have a certain passion for everything expensive, and often what motivates them the most is money. Not all Dwarves are cut for combat and adventuring, and some prefer to make their fortunes being master craftsmen or traders, but it is common for a Fortress Dwarf to leave their city right after Combat Training to try their luck as an Adventurer or a Shield, only returning after they think they have enough gold for a life of luxury.
As per PHB Mountain Dwarves, page 20