Merovingians in the 5th/6th century

[Flavivs Aetivs]

Depends on the kind of Lamellar. U-shaped lamellar (and of course rectangular plate lamellar) had been around since the Scythians of the 5th century BC, but wasn't widespread in Europe until the Sarmatians, who brought the technology down into Dacia and later with them when hired by Romans as Auxilia and later Foederati.

In the 4th and 5th century AD, you begin to see it being used in the Roman army, thanks to the large numbers of Alan and the Hunnic cavalry in service.

In the 6th century, the Avars and Langobards introduce D-shaped lamellar, a new kind which evidently must have been an improvement in some way over U-shaped lamellar. However, for some reason the Romans chose not to adopt D-shaped lamellar it seems, and the Byzantine Klivanion was still made with U-shaped pieces.

Frankly, that's all I know about Lamellar. I'm sure Alanus could elaborate, he's knowledgeable on steppe people use of lamellae.