на рубеже(At the cusp between the 18th and 19th centuries, enslaved Haitians emancipated themselves in a revolution from their French owners...; journalist and MP who lived at the cusp between the 18th and 19th Centuries – and also edited several volumes of Cobbett's writingsMaria Klavdieva)
на грани(figurative a point between two different situations or states, when a person or thing is poised between the two or just about to move from one to the other: those on the cusp of adulthood. NOED Alexander Demidov)