Sá vs Arch

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This is a list of United States Navy amphibious warfare ships. This type of ship has been in use with the US Navy since World War I. Ship status is indicated as either currently active [A] (including ready reserve), inactive [I], or precommissioning [P].

Ships in the inactive category include only ships in the inactive reserve, ships which have been disposed from US service have no listed status. Ships in the precommissioning category include ships under construction or on order.

Source: Wikipedia

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An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vaults, but a vault may be distinguished as a continuous arch forming a roof.

Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture, and their systematic use started with the ancient Romans, who were the first to apply the technique to a wide range of structures.

Source: Wikipedia