Beware Greeks bearing gifts.  Virgil wrote (in his Latin epic poem Aeneid)

I fear the Greeks, even though they offer gifts.

(The Penguin Dictionary of Quotations)
Brewer explains the expression a Greek gift as a treacherous gift, because in the Siege of Troy the Greeks used a wooden horse as a trick.

Talk like a Dutch uncle is a way of giving advice to a younger person.

Go Dutch means share the cost of an outing.

Dutch courage is an alcoholic drink used to give a boost to someone’s confidence.

It is strange that Dutch is the adjective used to describe people from the Netherlands (or Holland as we always used to call it).  Deutsch is German for German.  I have no idea why Dutch should be linked with any of these expressions, except that Britain and the Netherlands are only separated by the North Sea.  The few Dutch individuals I have been acquainted with are/were all delightful.  I have a photograph of a Dutch doll here.

Caesar’s wife must be above suspicion.
This expression is about the responsibility of the wife of a person in a position of power.  While no-one is perfect, history is made up of people who ignored this advice at their peril.

Too many chiefs and not enough Indians is an expression about a situation where there are more people trying to give orders and not enough to carry them out.  I imagine the Indians here to be North Americans.  Traditionally chiefs are pictured in enormous head-dresses and braves in smaller ones.  Here is a link to another post by a blogger who likes words and their derivations.

Living the life of Riley is an expression about someone having an easy time without having to make much effort.  The derivation is uncertain according to the link

Peter Piper picked a peck of pickled pepper is the first line of a tongue-twister.

An Aladdin’s cave is somewhere containing hidden treasures.  It was in a cave that Aladdin found a magic lamp, which he rubbed.  A genie appeared.  Aladdin became wealthy as a result of the genie’s actions.  (The story is in Arabian Nights.)  One of my memories of primary school is my home-made Aladdin costume which I wore to a fancy dress event.  My lamp was papier mâché covered in gold-coloured foil with a paper backing.  My Chinaman’s hat was similar gold coloured foil on a cardboard base.  I had a plait made from black wool.  My tunic was silver lurex and I had trousers.  I cannot remember what I wore on my feet to complete the outfit.

Achilles’ heel describes a weak point.  In Greek mythology the child Achilles was dipped into the river Styx in order to gain protection.  His mother held him by his heel, which was not protected and was his downfall.  The tendon down the back of one’s heel is known as the Achilles tendon.

There’s no law of the Medes and Persians that…
Laws of the Medes and Persians could not be changed.  Daniel 6:8  The story of Daniel in the lions’ den is often told to children.  If you have not read it as an adult click here.  Daniel 6