The phrase 'their multitudes' is correct and can be used in written English.
This phrase is often used to refer to a large number of people or things. For example, "The crowd cheered their multitudes as the fireworks began."
Over the past 30 years, optics well known to the physicist have been identified in their multitudes in nature.
These lists are striking not only for their multitudes but also for the glaring lack of a front-runner.
He groaned and defied their multitudes: "So what if there are more of you!" He celebrated their demise: "Bye, bye".
They set out from its borders in their multitudes, and soon the parks, the bars, the shopping centers were all but empty.
FROM OUR LEVANT CORRESPONDENTThe people of Teheran, in their multitudes, gave Ayatollah Khomeini a tumultuous welcome when he returned to Iran's capital on Thursday morning.
They were ultimately mortal — a point underscored in the opening lines of the Iliad, in which "strong souls of heroes" are "hurled in their multitudes to the house of Hades"— but fame gave them a kind of immortality.
What differentiates the Rams from recent offensive juggernauts is their multitude of threats.
Cephalopods are easily recognizable by their multitude of arms and tentacles.
Let others feel bad about their chicken wings — and their bottoms, their necks and their multitude of creases and wrinkles.
Mushrooms, in their multitude of shapes, colors, sizes, textures and tastes, have come to consume her existence.
Lexington and Madison Avenues, with their multitude of office towers and their narrow sidewalks, are the most congested avenues, he says.
