The construction materials on the island were stone, wood, lime, the claylike earth, reeds, and seaweed. In masonry they mainly used shale, marble rock, and ironstone. Typical features of those houses were and continue to be the arches or vaults that were built with a sort of slate called voltopetra. Windows and doors are frequently decorated with a marble frame, on which there are decorations in relief (lintels) that represent plants or birds. One extraordinary feature of the houses of Tinos is their marble-framed skylights. The houses of the villages that were built in the era when the Aegean Sea suffered from pirate raids were gathered around a fortress-like center built with arches and the roofs joined together, so that the villagers could use them to escape in case of attack. Even now, the basements of many houses are connected to each other, a fact that shows that the people also used to seek refuge underground.