By Kevin Anderson
BBC News Online in Boston
Some have begun calling the host city of the Democratic Party convention Fortress Boston for the unprecedented level of security.
National guard military police helped supplement local and state police
Authorities say they have no information of specific threats to attack the party conventions but are convinced that al-Qaeda is planning an attack ahead of the US elections.
They believe that al-Qaeda sees the potential to sway the US elections after the bombings in Madrid were interpreted by some as toppling the Spanish government and leading to a withdrawal of that country's troops from Iraq.
With more than 40 miles of roads being shut during the convention, Boston residents are braced for a week of disruptions.
Foreign and domestic threats
Just as they were in 2000, both the Republican and Democratic party conventions have been designated national special security events with the Secret Service overseeing security.
The US government will spend more than $125m for security during the conventions.
"Our goal is to deter any potential attack with multiple layers of security," Homeland Security Secretary Tom Ridge said during a tour of the 24-hour security command centre in Boston.
The Secret Service is in charge of security during the conventions
Armed Coast Guard boats patrolled the city's harbour and rivers.
Extra air marshals have been added to flights flying into Boston's Logan Airport, and only regularly scheduled flights will be allowed to land at the airport.
The Secret Service conducted a security sweep of the convention site that began on Friday and finished midday Saturday.
And while many of the details of the security preparations remain classified, the increased security measures were obvious in Boston.
Police with sniffer dogs are patrolling the area around the FleetCenter, where the convention will be held.
Snipers can be seen on rooftops near the convention site, and a network of more than 100 video cameras will provide surveillance around the convention site, authorities said.
Manhole covers have been welded shut, and rubbish bins and newspaper vending machines have been removed.
The security presence is strong with Boston police on many street corners and outside the hotels where delegates and media are staying.
Guests must provide photo identification and their room keys to guards outside of their hotels, and ventilation systems are being monitored at the hotels where 15,000 media and some 5,000 delegates are staying.
Emergency response teams are at the ready in case of a chemical or biological attack, and "chempacks" containing thousands of doses of antidote for such attacks have been sent to both Boston and New York, where the Republicans will hold their convention next month.
But the threats are coming not only from foreign groups like al-Qaeda.
The FBI field office in Boston also received an unconfirmed threat from a domestic terror group that it will be targeting the media and their vehicles with explosives or incendiary devices.
Media are being told not to wear their convention credentials openly in the city.
Residents brace for impact
Bostonians are preparing for a week of disruptions.
On Sunday, Raymond and Jennifer Banks took a stroll through the Boston Commons, a leafy park in the city centre, to see an anti-war protest and to get into the city before traffic disruptions began during the conventions.
On the commons, Boston police, park police and transit police helped provide security and even uniformed military police patrolled the park.
Mr Banks said the police presence there was 10 times greater than normal, in part due to an anti-war rally.
Police presence was heavy during an anti-war march on Sunday
"Usually, you see one or two cops patrolling around, now you see one or two every ten yards or so," he said.
The city has asked residents to stay home during the week due to expected traffic disruptions due to the heightened security, and the Banks are taking the advice.
Interstate 93, the main highway into and out of the city, will be closed during the hours the convention takes place each day because the motorway passes within feet of the FleetCenter where the convention will be held.
"It's a big bump in the road for life for normal Bostonians," Mr Banks said as the couple took a Sunday stroll through leafy Boston Commons.
Shutting Interstate 93 will cause traffic backups through all the suburbs of Boston he said, adding, "It's just going to be a nightmare."
Many of their friends and neighbours planned their summer vacations around the convention so they could be out of town.
Mrs Banks said, "We're personally not planning to leave the house all week."
Mr Banks added, "We're going to try to stay as far away from the main traffic as possible."