This paper traces the evolution of extreme illiquidity discounts among Treasury securities during the financial crisis; bonds fell more than six percent below more-liquid but otherwise identical notes. Using high-resolution data on market quality and trader identities and characteristics, we find that the discounts amplify through feedback loops, where cheaper, less-liquid securities flow to investors with longer horizons, thereby increasing their illiquidity and thus their appeal to these investors. The effect of the widened liquidity gap on transactions costs is further amplified by a surge in the price liquidity providers charged for access to their balance sheets in the crisis.