Pse, translate some words

In an article I read that Emperor Darius knew that some of his peoples (the Galatas) ate their dead; other, the Greek, dit not. Чтобы преподать урок культурного взаимопонимания, Дарий однажды пригласил бывших в тот день при дворе греков и српосил, за какие деньги они согласились бы съедать своих покойников.

The words italized are where I have doubts. I have seen always бывший with other words: "ex/former-minister" and so on. He invited the Greek near the palace or invited the бывших near the palace of the Greek ?. Бывший is the trouble.

Thanks

"бывших в тот день при дворе"
"greeks who were at court that day".

it goes... "greeks "being" at court that day". -- literally.

Thanks for your quick help.