MANITOWOC - Four men were arrested after breaking into a cement plant overnight.Manitowoc police say a silent burglar alarm was tripped at the St. Mary's Cement Plant, 1801 Spring St., around 1:15 a.m. The first officer on scene thought he briefly saw the silhouette of a person inside before the silhouette disappeared into the darkness. Police surrounded the building, and a small team of officers went inside to search, with others keeping watch on the outside.When officers got to the top floor, they found and arrested three people who were hiding. The fourth person was found on the roof.The four arrested were all Manitowoc men in their teens and early 20s. They told police they went in through an obscure opening and wanted to explore the architectural design of the old building.The men were ticketed for trespassing and underage drinking and released.