Symbolism, Imagery, Allegory
A Tomb with a View
The Mannon home isn't like what you'd expect to see on MTV's Cribs. Like most rich folks, the Mannons love showing off their money, but the way O'Neill describes this mansion is more than just proof of just how loaded the family is. O'Neill's stage directions describe a "large building of the Greek temple type that was in vogue for the first half of the nineteenth century. A white wooden portico with six tall columns contrasts with the wall of the house proper which is of gray cut stone."
A whole lot is going on there. First of all, the comparison to a "Greek temple" is no coincidence. It's yet another way that O'Neill is trying to tell us that this play is based on one of the greatest ever works of Greek tragedy, The Oresteia—he probably figured it would be better than having the Mannons running around in tunics and sandals.
Then there's how the house is described. It's basically got two parts—the one that looks super fancy and awesome and is the first part that people see (the portico). Then there's the part that's dull and ugly (the part of the house made from gray cut stone). It's almost like the house has a false front that hides its real ugliness, just like the Mannons have put on a false front all these years to hide their nasty secrets and the hideousness that's gone down inside those walls.
Finally, there's the way that certain characters, like Orin and Christine, describe the house using imagery connected with death, dying, and burial. Christine calls it a "tomb" when she and Lavinia are talking in Homecoming (Act 1). As a Mannon by marriage and not by DNA, she seems to hate the house the most:
I've been to the greenhouse to pick these. I felt our tomb needed a little brightening. (She nods scornfully towards the house.) Each time I come back from being away it appears more like a sepulcher! The "whited one" of the bible—pagan temple front stuck like a mask on Puritan gray ugliness! It was just like old Abe Mannon to build such a monstrosity—as a temple for his hatred! Forgive me Vinnie, I forgot you liked it. And you ought to. It suits your temperament. (Homecoming, Act 1)
Orin also remarks to Peter that he thinks it's weird how much the moonlight makes the house look like a "tomb." Describing the house in this way both foreshadows the deaths to come and reminds us—in The Hunted, at least (Act 2)—of the fact that at least one character has already died there. The house represents secrets and death.