A primary droid foundry was a battle droid factory that was built on the planet Geonosis during the Clone Wars. It was destroyed by Jedi Padawans Barriss Offee and Ahsoka Tano in 21 BBY.
In 21 BBY, Senators Rush Clovis of the InterGalactic Banking Clan, Lott Dod of the Trade Federation, and Archduke Poggle the Lesser invested in a secret new droid foundry on Geonosis. Unfortunately Senator Padmé Amidala discovered a hologram during her diplomatic mission to Cato Neimoidia. Amidala was able to steal the hologram as well as the factory's tactical coordinates and gave them to the Jedi Council.
B1 battle droids could be built in the factory.
Poggle and his tactical droid, TX-21, took command of the factory when the Republic attacked Geonosis and destroyed the ray shield generator protecting the factory. By the time the Republic were in front of the Factory, Poggle had ten garrisons of B1-series battle droids ready to be deployed. In addition, twenty new Super tanks were ready deployed. Poggle deployed the garrisons and super tanks against the Jedi General Luminara Unduli's 41st Elite Corps and Anakin Skywalker's 501st Legion. During this time, Jedi Commanders and Barriss Offee and Ahsoka Tano were able to infiltrate the factory through the catacombs and plant bombs on the factory's . Unfortunately, a Geonosian informed Poggle and TX-21 of this and took a super tank to stop them. The Jedi commanders were able to destroy the super tanks drivers, but lost the bombs to the Geonosians. Offee and Tano decided to use the super tank to destroy the generator and factory. They survived the explosion and were found by their masters.