The road that ran along the crest of the hill above the the north bank of the River Thames came to known as the Strand. Great families established grand estates between the road and the river.
While the river was the principal transport artery, minor roads gave access to land along the Tyburn and below the roman road to Bath that is now Oxford Street. The road now called Charing Cross Road linked the Strand to that Roman Road and created a busy intersection at Charing. Over the centuries, these roads became more important, particularly after Westminster became the site of the royal presence near London, when Edward the Confessor invested in the Abbey and the Palace.
Perhaps the first significant happening was the funeral procession for Eleanor of Castile, wonderful Queen of Edward I. The King had a monument Cross erected here and at eleven other sites where the procession spent the night on the March to the funeral held at Westminster Abbey. Placing of the 'Eleanor Cross' at Charing may well have been the reason this area is now known as Charing Cross.
King Henry VIII received the riverfront estate known as York Place from Cardinal Wolsey (circa 1530) and it was built into the principal royal residence, and eventually called Whitehall Palace. The name Whitehall continues to this day, as the name of the thoroughfare between Parliament Street and Trafalgar Square. It is said that the traffic on Sunday was terrible, what with everybody north of Whitehall going to St Margaret's Church, so good King Henry ordered a new church to be built besides the Mews. The church we see today is the second on the site, and it is called St Martin's-in-the-Fields. The land north of the Charing Cross intersection was used as a Mews for the palace's courtiers for nearly 300 years, until the Prince Regent, the eventual George IV, had most of the area redesigned, including a square and great monument to honour Admiral Nelson and the great victory over Napoleon's navy, off the spanish coast near Cape Trafalgar. It is no small coincidence that this was located a few meters from the Admiralty complex, west side of Whitehall.
In the many decades since, Trafalgar Square has evolved into a central gathering place as well as the central transport hub for London.