Archaeologist Anton Seiler inspects one of the foundations where there once was a wooden pole at an excavation site of the country's largest Iron Age monument in Old Uppsala, Sweden

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 (1 kilometer) 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 (6 meters)," 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."

She said the pillars are believed to have been at least 23 feet (7 meters) high. Bones found in some postholes indicate animals had been sacrificed there.

Old Uppsala is known as a center for Norse religion, where believers gathered to sacrifice animals to gods such as Odin and Thor. The colonnades were found near a famous burial site where the three Iron Age kings Aun, Egil and Adils are believed to be buried.

Beronius-Jorpeland said written testimonies from medieval times describe the city as a place for large pagan "blood ceremonies" and religious feasts.

She said she believes there may be more colonnades in the area and archaeologists will continue to excavate and analyze the findings.

Explore further Work on new railway line digs up London history (Update)

© 2013 The Associated Press. All rights reserved.