STOCKHOLM (AP) — Archaeologists in Sweden said Thursday they have unearthed the remains of unusually large wooden monuments near a pre- Viking Age burial ground.

As archaeologists dug in preparation for a new railway line, they found traces of two rows of wooden pillars in Old Uppsala, an ancient pagan religious center. One stretched about 1,000 yards and the other was half as long.

Archaeologist Lena Beronius Jorpeland said the colonnades were likely from the 5th century but their purpose is unclear. She called it Sweden’s largest Iron Age construction and said the geometrical structure is unique.

“It is a completely straight line and they have dug postholes every 20 feet,” she said. “They have had an idea of exactly where this line is going and where to build it. It is a fairly modern way of thinking and we don’t have many traces of these sorts of constructions from that time.”