Expanding its presence in the Boston market, Denver-based Apartment Investment and Management Co. (Aimco) has acquired 11 garden and mid-rise apartment properties for $500 million from New England developer Thomas J. Flatley. With the purchase, Boston becomes Aimco’s third largest market.

"In addition to the existing cash flows, we believe that there are excellent upsides available from the improving Boston market," said Terry Considine, Aimco chairman and CEO, in a statement. "The low density, campus-like settings are, literally, irreplaceable."

The average monthly rent for the 4,323-unit portfolio is $1,263, with occupancy at 94.4%.