Occupying the original parlor level and third floor, Unit 8, 9, 10, 11 preserves rich historical details and spaces that bespeak Blanchard's socioeconomic standing and Eastern mercantile travels. The home includes seven fireplaces.

Combining two units may create a condo that no longer feels small, but merging four will yield a unit that truly feels like a masterful home. Just check out Unit 8, 9, 10, 11 at 144 Beacon St., where four smaller units were unified into a 3,970-square-foot magnificent duplex.

It creates enough splendidly scaled spaces, ace amenities, delicate details and fine finishes to feel like the Back Bay townhouse the mansard-roofed brownstone was originally constructed to be.

Built in 1859-1860 by Edwin Adams for East India shipping merchant John Adams Blanchard, 144 Beacon St. was converted into 12 condos in 1982. In 2008, they were integrated into five deluxe duplex and floor-through units.

Occupying the original parlor level and third floor, Unit 8, 9, 10, 11 preserves rich historical details and spaces that bespeak Blanchard’s socioeconomic standing and Eastern mercantile travels. The home includes seven fireplaces.

This meeting of East and West greets you right at the door as the foyer introduces a barrel-vaulted, mahogany-paneled corridor to the living room where a carved oriental lantern hangs from a ceiling of geometric moldings on central axis with the corridor, foyer and door. Adding to the Asian aura is a broad bay window with leaded casement panes and white fabric Roman shades recalling Japanese rice-paper screens.

European details include an elaborately carved limestone fireplace, over-mantel paneling with fluted wood pilasters and scrolled capitals, a leaded-glass triple casement window over a built-in bookcase, mahogany-paneled walls and a crown molding with triglyph bracket reliefs.

Over the entry is a pediment carved with Grecian urns and a crowning eagle in a feathery scallop.

The foyer’s marble-tiled floor, laid on the diagonal with square wood inlay accents, continues rightward into a powder room with a pedestal sink and paneled wainscoting. The corridor’s paneling conceals a coat closet and a laundry room with a Bosch washer and dryer and slop sink. A small library with a built-in desk and bookcase connects the living room to the dining room, which the foyer also accesses.

European elaboration also reigns in the dining room. The oval-paneled ceiling’s leafy central molding is chandelier-ready. The arched white marble fireplace mantel with squared rosettes and recessed paneling forms harmonious symmetry with the arched book/china cases on either side. Paneled wainscoting runs all around the room.

A double French door opens to a private terrace with Esplanade and Charles River views – ideal for sunset aperitifs or al fresco dining in warmer months. A lavishly scrolled stairway rail with gilded leaf motifs ascends to the bedroom level.

Under the stairway, an arched entry connects the dining room to the European kitchen. Paneled off-white cabinetry incorporates a Sub-Zero refrigerator. Parallel tiger-granite counters and backsplashes encompass a Thermador Professional four-burner gas range on the right side and a farmer’s sink on the left. This counter angles leftward along two Sub-Zero wine coolers facing a granite island counter with square-columned seating areas.

The island is open to a sunny family room with paneled wainscoting, ceiling and crown moldings, a built-in cabinet/entertainment center and a classic fireplace mantel with urn relief and fluted engaged columns. Two windows with angled paneled recesses, scrolled cast-iron rails and unobtrusive Runtal radiators let in the elegance of Victorian Back Bay architecture.

The third front window sheds the same light and views on the adjacent study, where a square-columned white marble mantel frames a fireplace of burgundy Chelsea tiles with leaf motifs. If this is used as a guestroom, a full marble bath is handy off a hallway from the family room to the dining room.

The staircase grandly ascends past arched statue/vase niches to the bedroom level. The master suite begins with a smaller bedroom with an arched marble fireplace carved with fruit-and-nut motifs and a closeted wet bar with a granite counter and fridge. This room is suitable as an office, home gym, entertaining space or nursery.

The adjacent hall privately accesses the building’s common stairway and elevator via a door with a frog-on-leaf bronze knocker.

From here, a dressing hall with a large mirror and four double-door closets, one built in with a makeup vanity complex, leads to the four-piece marble bath with a soaking tub, shower with three showerhead options (rain, fixed, hand-held) and a twin-sink vanity. Two large mirrors give palatial dimensions to your bath.

The dressing hall terminates in the grand master bedroom, where a broad bay window fills the room with light and offers an expansive river-view terrace through a central French window. Fabric paneling in the king-size bed niche adds comfort to reading in bed.

Two other bedrooms with arched marble fireplaces and Beacon Street views share a full marble bath with benched steam shower. The third bedroom can be a study or home gym.

The fourth bedroom has a sizable walk-in closet. Flower/fruit relief carvings adorn its fireplace mantel.

The building’s common entry areas match the unit’s elegance. The vaulted vestibule’s facing arched mirrors create an illusion of infinite space. The lavishly paneled lobby greets you with a black-and-white marble floor and a hotel-style sitting area with a mirror wall.

A pineapple-crowned newel post wrapped in a spiraling stringcourse of beads initiates the banister of twisted balusters and pineapple-topped posts that regally escorts you to your unit.

Offered at $7.1 million, Unit 8, 9, 10, 11 at 144 Beacon St. shows what the breaking down of barriers can do to make a condo a castle to keep. For a private showing, contact Tracy Campion of Campion and Company at 617-203-6176 or TCampion@Campionre.com.