Stronghold (noun)

1. A place that is strongly fortified, defended, or protected.
2. A place or position that is strongly defended or protected in a particular area or sphere of activity.
3. A place where someone or something is firmly established and difficult to dislodge.

Origin:

Middle english: from old english strong (adjective) + hold (noun), translating latin arx, -cis.

Examples:

1. The castle was a stronghold for the king's army.
2. The party's stronghold in the region.
3. The company was a stronghold in the market.
4. The union's stronghold among the workers.
5. The stronghold of tradition in the countryside.