The city that faced the open sea

Start with geography

A sheltered harbour with the Atlantic outside it

The Tagus widens into a broad basin before narrowing to meet the sea. That gives Lisbon deep, sheltered water big enough to assemble and repair a fleet, only a few kilometres from the open Atlantic.

Compare that with a Mediterranean port, which is sheltered but must pass a strait to reach the ocean. If your strategic question is 'how do we sail down the coast of Africa and keep going', an Atlantic-facing estuary is the right address, and the Mediterranean's ports are the wrong ones.

Answer the check to continue.