SARJAH, Syria — Abdulkader Darwish did not go far after a Syrian military aircraft dropped a bomb near his house last year, prompting him to gather his family and flee. He ventured with a shovel into the local olive groves. There he dug through the sealed entrance to an abandoned Roman cave.

Nine months on, dozens of members of the extended Darwish family have passed a cycle of the seasons crowded together in the damp and almost unlighted space. They have gained neighbors all the while, residents of a subterranean community in Syria’s northwest.

“There are many caves here, a line of caves, like an ancient village,” Mr. Darwish said as he huddled with several children inside. “All of them have been cleaned and are now occupied. There is not a vacant cave.”

As the bloody civil war between the government of President Bashar al-Assad and the opposition enters its third year, and Mr. Assad’s military continues to pound neighborhoods aligned with the rebels, uncountable Syrian families are waiting out the violence in the caves of bygone times. They are part of the four million people who the United Nations estimates have been forced by the war from their homes, a displacement that seemingly grows each week.