Pedestal of Truth (3.5e Equipment)
From D&D Wiki
A Pedestal of Truth is a large obelisk erecting from the ground, covered in symbols and inscriptions. It is about 6 feet tall, and made of solid rock, and often built into the ground. It radiates a Hallowed aura and a "zone of truth" effect for up to one hundred square meters thats about 300feet (roughly).