In the waist-coat pocket of the elegantly dressed but crushingly poor Solly Two Kings, where most men would keep a watch, Solly has a short, thick length of chain that once kept him enslaved. Nothing informs August Wilson’s play, or the dramatist’s entire cycle – one play for each 20th-century decade - more emphatically than that piece of chain.

All playwrights stake out their territory. But few dramatic landscapes are as well defined as that of Wilson, whose work chronicles the African-American experience. As does the Tricycle’s season of African-American plays, which started with a revival of Abram Hill’s underwhelming Walk Hard but which receives a powerful boost with the penultimate play in Wilson’s epic project.

As with most of the works in Wilson’s cycle, Gem of the Ocean is set in the Pittsburgh slum Hill district of the writer’s youth. Setting his drama in 1904 makes this play his chronologically closest to slavery. Here, Wilson blends realism with myth, personified by the 285-year-old Aunt Tyler (Carmen Munroe) who runs a ramshackle house of sanctuary, “washing the souls” of good people who have done bad things.

Enter Citizen (Kobna Holdbrook-Smith), whose mother named him after the abolition of slavery and who is desperate for redemption after allowing someone else to take the rap for his crime. In exchange for helping the house’s sentinel Eli (Lucian Msmati) build a wall in the yard, Aunt Tyler helps Citizen face his demons by taking him to the mythical “city of bones”.

It’s here that Wilson’s play launches into a climax of ritual as Tyler and the other members of the household chant the sceptical Citizen into an epiphany. And it’s here too that Wilson’s drama, and Paulette Randall’s superbly acted production, is presumably meant to reach its theatrical height.

But the power of Wilson’s eloquent writing lies more in realism than myth. When Caesar (Patrick Robinson), the hated local lawman and landlord, describes his struggle against white prejudice and black resentment, the play fizzes into life as its most loathed character is made human.

And it’s when Joseph Marcell’s dignified Solly – who ekes out a living selling dog-shit fertilizer - relates the reality of a hard-won but bitter freedom that brought about poverty and exploitation, that the play witnesses the struggle for dignity by a people shattered by slavery. A dignity that Wilson, who died last year of liver cancer, did so much to form.

- John Nathan