Dratan
Castle Siege is a contest to decide the owner of the Pyramid which is located in southwestern Dratan. The first time the Pyramid was up for grabs, there were only attackers. At this point in time, however, the Tombs on all servers are owned, so for each siege there are both attackers and defenders. The owners of the Pyramid get to control the settings for the Tomb of Theos. Read on to find out more about these roles and how the siege actually happens. Important Note: Any guild can only own one castle. This means if your guild won the Merac Castle Siege, you cannot participate in Dratan Castle Siege, and vice versa.
Registration 
To register for Dratan Castle Siege, your guild master must must talk to the NPC outside the main outside gate: Steward Tot.
Note: Your guild must be level 6 or higher.
Attacking Guilds: The brave souls that have chosen to take on the defenders in a bid for Tomb ownership.
Defenders: The guild defending the Pyramid.
Mercenaries: Loyal to no guild, these mercenaries can attack and kill both attackers and defenders.
Note: PK mode can be turned on during the siege, but players may or may not lose experience if killed by someone with PK mode on. You will loose experience if you are killed by someone with PK mode on before you enter the two statues (coordinates: 223, 2349). Once past those statues, you will not lose experience from players with PK mode on unless you are on the stairs of the pyramid and die with PK mode on or are red.
Attacking
All guilds except the defending guild take on the role of attackers and all compete for ownership of the Pyramid.

Attacking guilds must first destroy an Eye of Barrier (the single outside first gate, pictured to the left) to open the outside gate. Once the Eye of Barrier is destroyed, the main gate will open.
The main gate is controlled by a tower located not too far away. This tower must be destroyed in order to bring down the main gate.
Once inside there are two more gates on either side of the Pyramid, which also have Eye of Barriers (on the left and right side of Pyramid). These must both be destroyed in order to approach the Crystal of Sympathy.
The Crystal of Sympathy is located atop the Pyramid. Up to 5 attacking guild members can approach at once. You must click on the on the crystal and begin gaining sympathy. Gaining full sympathy takes 3 minutes. While gaining sympathy you cannot move, use skills or use healing potions, otherwise you must begin over again.
Successfully gaining full sympathy earns you ownership of the Pyramid. Dratan Castle Siege lasts 2 hours so the Pyramid will undoubtedly change hands several times. Whoever holds full sympathy when time runs out is declared the winner!
Defending The current owners of the Pyramid take the role of Defenders and have the advantage of setting up Pyramid defenses which come in many forms.
Towers 
Towers are one form of defense that the defending guild can employ. Before the Dratan Castle Siege begins, the defending guild's guild master must speak with the Master Tower located outside of the first gate. The Master Tower allows the defendering guild to set up towers. Clicking on other towers as a defender will give you the option of repairing them.
Towers can be used for attack, defense, and teleporting and come in 6 different varieties.You get to make upto 1 tower of each type for free, but you can create more for a fee.
Attacking Towers
Attacking towers (pictured to the right) come in three forms: short distance, long distance, and magic attack. Short distance towers attack enemies near the base of the tower. They are a good place for defending fighters to stand near while holding back those wishing to take the Pyramid. Long range towers attack from afar, but do less damage than the short distance towers. Magic attacking towers are short range towers that attack with magic. These do equal damage to their physical short-distance counterparts.
Defending Towers Defending towers (pictured to the right) come in three forms: decrease speed, decrease stats, and posion. Decrease speed towers have medium range and decrease the enemies movement and attack speeds. Decrease stats towers debuff the enemy lower their attack. Poison towers do damage over time to enemies.
Warp TowersWarp towers decrease the resurrection time of fallen defenders and allow the defenders to easily move to different sections of the pyramid.
Upgrade TowersUpgrade towers give you the ability to upgrade the attacking/defending/warp towers' hit points and increases the strength of the towers' abilities for a fee
Repair TowerRepair towers repair the Master Tower.
Upgrade GateUpgrade gates let you upgrade the durability of each gate (the Eye of Barriers mentioned before) making it harder for attackers to take them down.
Guardians 
Guardians are another form of defense available to the defending guild. Guardians are NPC’s that can be purchased before the siege begins. They can be placed anywhere within the Pyramid area except for the top of the Pyramid. These guardians will attack anyone who comes within their range except for defenders and come in two varieties: As a Sphinx Spear Man or a Sphinx Guardian. Both are level 100 creatures and are pictured to the right. You may only have 10 of each kind of guardian.
Note: Defenders should know that if the Castle changes hands during the battle, all defenses are handed over to the new owners of the castle including towers and guardians.
The holders of Dratan Castle will also
control the dungeon located inside the Pyramid, known as the Tomb of Theos (Tomb for short). The owning guild's guild advisors and guild master can set the Tomb's difficulty level, entrance fee, and the amount of gold which is taxed from kills made in the tomb. This money is transferred straight to the owning guild's vault.
Many Thanks to:
GMAracton for the original post
BeazleBub and
purpleflame for helping put this guide together
Tiberias for updates