"Lothal was probably the most important port after Dvarka drowned. Both were gateways to Sarasvati lands and dominated maritime trade west and south. At the head of a now diverted River Sabarmati tributary, its 12.2-metre thick walls, protection against floods, enclosed a modest seven hectares (17.29 acres) with habitation outside. The massive 214 metres long, 37 metres wide, 4.5 metres deep dock, originally probably deeper was built with over a million kilndried bricks. Eighteen to twenty metres long and four to six metres wide ships could enter with two passing each other. Away from the main current to avoid siltation, lock gates controlled a channel to the estuary at high tide. Estimated to hold 30 ships of 60 tons, or 60 of 30 tons each, it indicates heavy traffic. Navigational instruments to measure angles of the horizon and stars and stone anchors have also been found. A 3.5 metres long wharf, raised against flooding, connected the dock to a 64-room warehouse, containing merchant seals. Each Indus-Sarasvati merchant had a seal to identify and label imports and exports, authenticating ownership, many found in Mesopotamia indicating their main trade outlet."