Fortification in faction warfare.
Fortification in faction war involves having a stockpile of plex fighting ships in a location, and having enough pilots or allied pilots to come fly them when under siege by an enemy. Plex fighting ships are usually frigates and destroyers, which are fit cheaply so they can be lost by the hundreds.
This stockpile of ships should be in the system being defended for maximum strength, or be located one jump away for a weaker defence.
The stockpile can be in a station, citadel or POS. A POS is very difficult to organise so we can generally ignore that possibility.
A station is the easiest staging option, but it is vulnerable to loss if the enemy can conquer the system. A concerted offensive can flip an undefended system in about 2 days. If the system is at 50% vulnerability before the offensive it can be lost in one day.
So to defend a station stockpile the system needs to be kept at a low level of contention at all times, so that there is longer than one day to call on allies for a strong defence. Attacking a defended system usually results in the loss of over a thousand Plex fighting ships by both sides.
The other stockpile option is a citadel. A citadel is invulnerable to system loss. However it is vulnerable to an attack by large fleets or capital ships. However it is only vulnerable for a few hours each week and it requires 3 battles over the course of a week to destroy it.
In short a station is can be captured by 48 hour assault by a large number of players in low skillpoint ships like frigates and destroyers.
A citadel can be destroyed by a medium sized force of expensive high skillpoint ships such as Battlecruisers, battleships or capital ships, in 3 battles over a week.