This is the 10954th most frequent Russian word.
выстраивались
"Выстраивались" means "were lining up" or "were being arranged."
'Выстраивались' is used metaphorically here to describe books being arranged in an orderly fashion.
Книги аккуратно выстраивались на полке.
Books were neatly lined up on the shelf.
The word 'выстраивались' is used here to describe the action of forming a line sequentially by individuals.
Перед входом в театр люди выстраивались в длинную очередь.
People lined up in a long queue in front of the theater entrance.
The word 'выстраивались' illustrates the action of soldiers organizing themselves into a formal arrangement.