Beth Allen and Merrily Welch know Boston and know it well.

The longtime friends have traveled to the city just about every year since the dawn of the millennium to race in the prestigious Boston Marathon, the oldest of its kind in the country.

“I don’t know every nook and cranny of the race but I’m very, very familiar with the course,” said Allen, 53, of Farmington, who will run her 10th Boston Marathon and 23rd overall. “I don’t have any trepidation with the course at all.”

Added Welch, 46, of Temple, who is running in her eighth Boston Marathon: “It has become part of our lives. We go way back with the Boston.”

The annual Boston Marathon is Monday. About 500,000 spectators are expected to watch the more than 35,000 runners who will depart from Hopkinton and finish near the John Hancock Tower in Boston’s Copley Square.

The elite field will compete for an $806,000 purse.

The marathon brings together elite and novice runners from different backgrounds and locales.

Some, like Allen and Welch, are marathon veterans who have their training and preparation down to a science.

Others, like Magen Ellis, 22, of Farmingdale, and Sarah Doscinski, 35, of Vienna, are running their first Boston Marathons.

“I’ve raced in just one marathon before, and I used it to qualify for Boston,” said Ellis, referring to the Sugarloaf Marathon held in May. “I’ve always been attracted to longer distances. Boston is the oldest one in the world and probably the most elite. There is a lot of prestige. It’s always been a long-term goal of mine. I was more attracted to run the Boston than running a marathon.”

Ellis is a senior at the University of Maine. She ran for the Black Bears in her freshman year before she decided to focus on school work and her job.

“I ran in college but once I stopped collegiate running I really wanted to pursue something else, something I had never done before,” Ellis said. “I had my sights on a marathon.”

She’s never stopped running and last May decided to run the Sugarloaf Marathon.

Ellis finished 55th overall with a time of 3 hours, 16 minutes, 15.4 seconds, which qualified her for the Boston Marathon.

“As soon as I crossed the line I felt miserable, physically and exhausted,” Ellis said. “I had the intention of never running a marathon again. But when I found out I had qualified for Boston, I forgot about what I said.”

She followed up the Sugarloaf Marathon with a strong showing at the Kennebec Rail Trail Half Marathon in June, in which she set a women’s course record with a time of 1:27:22.

“That helped my confidence,” she said.

Like Ellis, Doscinski — the University of Maine at Farmington cross country coach — is also running her first Boston Marathon.

She’s competed in two previous marathons.

“I’m a little nervous, but I’m more excited,” said Doscinski, who often trains with Allen and Welch. “It’s such a big race that I’m looking to go there and enjoy it. There should be a ton of people there. It’s going to be exciting. I know it will be different than the other two I’ve done. It’s such a huge race, and (Welch and Allen) shared with me that it’s just so totally different from anything else.”

Welch and Allen train together often and run at least two marathons each year. They’ve competed in marathons in New York, Philadelphia and even California.

Both say they run well together, with each picking up things during long runs that the other doesn’t see.

It’s all part of their running technique.

“Every year there’s something that stands out at Boston,” Welch said. “We both bring strengths. I’m a very a competitive runner, and so is she. She notices things, like signs. I notice people and the colors of T-shirts. We come from different perspectives, and we’ve given that to each other.”

Added Allen: “We’ve trained for multiple Bostons. We typically start training January. We do a 16-week training program. We train on our own during the week and build up distance. We then get together on weekends and do long runs.”

Welch and Allen ran their first Boston Marathon in 2000 — a year before they met.

They ran it together in 2001 and only missed the last two years when the fields filled before they could register.

Now, they are back and ready for the grueling streets of Boston and its surrounding communities.

“We make this a family affair,” Welch said. ” When we started with the Boston, we did it to be able to say we did it. It’s the king of marathons. But when we did it, we got hooked and we just kept coming back. Now, it’s on the docket for every year.”

Bill Stewart — 621-5640

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