As the Democratic National Convention opens Monday, the city of Boston will be under an unprecedented $60 million security curtain. Federal agents have inspected manholes, welding them shut for safety. Mailboxes and most trash cans have been removed from businesses around the FleetCenter, where more than 4,300 delegates and 15,000 members of the media will gather for four days. Interstate 93, the main highway on which traffic flows in and out of the city, will be closed during convention hours because it passes within 10 feet of the convention site. About 40 miles of roads will be closed in total. Full Story