Lighthouse

Alexandria, the early 3rd century BC. The Pharos rises by the harbour, built of white marble. Perhaps 120 to 140 metres tall. No lighthouse of antiquity is more famous. Earthquakes bring it down in the 14th century. In 1480 the Ottomans build a fortress on its remains.

Sweden has to wait. In 1651 a light is lit on Landsort, at the far edge of the Stockholm archipelago. It goes out in December, when the ice sets in. The next year the Admiralty takes charge of the country's lighthouses.

In 1686 Landsort's present lighthouse is finished. In 1719 the Russians come and burn Landsort. The lighthouse survives – its walls are a metre thick.

Then technology takes over. Landsort gets electric light in 1938. In 1963 it is automated and the keepers move ashore. Lighthouse after lighthouse goes the same way.

But who says a lighthouse has to stand by the sea? Lake Vättern is big and can be treacherous. In the second half of the 19th century, light after light goes up along its shores. Vadstena gets its own in 1889, at the far end of the pier. An octagonal timber tower, seven metres tall. Three white flashes every nine seconds. That is its signature. It tells the helmsman which light she is looking at.

Daymark. A sea mark without a light. The daymark is seen by day, the lighthouse by night.

City gate. Both can have towers and thick walls. But the city gate guards a road in, the lighthouse guards a shipping lane.