Temple Bar

The last remaining gatehouse of the City of London, it has not stood in its original location for more than a century. All the other City gates - Roman and Medieval - are now remembered only in street names or districts (such as Bishopsgate, Moorgate, Aldgate, Aldersgate).
Temple Bar marked the western entry point to the City - originally just where Fleet Street meets the Strand. As it was the route to the Royal Palace of Whitehall, Temple Bar became the only place where the monarch could enter the City - having to pause to be invited in by the Lord Mayor. After the defeat of the Spanish Armada, Queen Elizabeth I presented the Mayor with a jewel encrusted sword. Ever since, the Mayor offers the monarch the sword when they enter the City on state occasions.
The name Temple derives from its original proximity to the legal district of that name.
Initially, it would have simply been a chain between two wooden posts that could be drawn closed when necessary.
This was then replaced in 1351 with a large wooden arch, which had a prison in the chamber above the roadway.
When this fell into disrepair, King Charles II commissioned Sir Christopher Wren to build a new arch in stone. We only know of Wren's involvement as his son found the original drawings after his death.
The new arch had four statues set in niches - King James I and his Queen, Anne of Denmark, facing towards the City, and King Charles I and II facing Westminster.
The gate was one of those which used to display the severed heads of traitors. You could hire a spyglass for a penny to get a closer look.

In the mid-19th Century the gate came under threat with the building of the Royal Courts of Justice and with the need to widen the road - due to the increase in traffic on this main east - west route. Rather than demolish it, it was decided to systematically dismantle it, stone by stone - all numbered - and put the pieces in storage near Farringdon Road. Some 10 years later, it was bought by Lady Meux and reassembled on her estate, Theobolds Park, in Hertfordshire. She was an interesting character - a banjo-playing barmaid who married into a wealthy brewing family.
Sadly, over time, the gatehouse fell into disrepair. A campaign was established to bring the gatehouse back to the City of London. In 2004, the official opening ceremony was held for the Temple Bar at its new location - in Paternoster Square in the shadow of St Paul's Cathedral.

Today, the original location for the Bar is marked with a monumental plinth topped by a dragon or griffin, in the middle of the road next to the Royal Courts.