Coelestis' Ramparts

You conjure a fortress in range that lasts for the duration. You choose where its one gate is located. Its entrance  is 5 feet wide and 10 feet tall and is protected by a gate made of thin beams of light. You and any creature you designate when you cast the spell can enter the fortress as long as the gate remains open. You can open or close the gate if you are within 30 feet of it. Any creature who tries to pass through the gate while it is closed must make a Constitution saving throw, taking 25 (5d10) Lightning damage on a failed save or half as much on a successful one. The beams of light vanish when the gate is open.

The fortress is a vast structure with stone walls which are 5 feet thick and up to 20 feet tall and have walkable pathways along the top. Any walls you designate may have a corridor with arrow slits below the top if you wish. You can create any floor plan you like, but the space can’t exceed 50 cubes, each cube being 10 feet on each side. The place may be furnished and decorated as you wish. The fortress contains enough rations to feed 20 people for 10 days. It also contains up to six siege weapons (your choice of a ballista, a trebuchet, or a cannon; your GM may edit this list as appropriate for the campaign), which can be placed wherever you wish, and the fortress generates as many nearly invisible soldiers as needed to man the siege weapons at maximum efficiency (but no more). These soldiers are immune to all damage, but cannot attack or take actions except to use their assigned siege weapon.

The space taken up by the fortress, including empty space contained within it, replaces solid material that was there before the spell was cast. This material returns when the spell ends.

The fortress has up to two flags, which can appear however and wherever you desire.