Panic swept the financial district yesterday as the greatest sell-off in market history wiped out billions in stock values. From the opening bell to final close, exchange floors were scenes of wild disorder. Prominent bankers held an emergency meeting in an attempt to stabilize the market, but their efforts did little to halt the downward slide. Crowds gathered outside the exchange in tense silence, watching the bulletin boards as fortunes disappeared in minutes. The aftermath of this black day remains to be seen, but experts fear a long road to recovery.