Under Siege - not the Steven Segal kind though

So, we're under siege. My 4th edition party has found itself defending the crumbling Hillsfar from a horde of Lamia-loving cultists, dominated rabble and of course... said Lamia.
So far, we've organised the city guard, completed hasty repairs to the walls and towers, created a second line of defence and formed a citizens' militia.
A quick sally through the sewers also knocked out an inflitration attempt and raided the cultists' camp.
Next session will see the horde descend on the city - and hopefully we can hold them back
But it got me thinking - organising frightened townsfolk, throwing together walls ala the Seven Samurai and generally finding yourself caught up in someone else's problem is pretty much par for the course for D&D.
All in a day's work for adventurer.