Why is 6 afraid of 7?

Once upon a time, there was a castle on a square island. The entire island was surrounded by a 14m wide trench. The Romans had wanted to invade the castle and had brought a few wooden planks along with them to facilitate themselves in crossing the moat. The planks were however found to be only 13m long.

The Romans still managed to cross the trench. How did they do it?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

I know a nine-letter word having only one vowel.
Do you ?

John bought a new car. He has a habit of eating ice cream from a particular ice cream shop while returning home from office. Whenever, he eats strawberry ice cream, he faces no problem. But whenever, he eats chocolate ice cream, the car starts giving problem. At first, he thinks, it is just a co-incidence but when this awkward incident happens for 3-4 times, he reports this problem to the company.

The mechanic of the company checks but finds no problem at all. The next day, when he stops by to eat chocolate ice cream, the car again starts giving problem.

Can you find the possible reason?

Four men were in a boat on the lake. The boat turns over, and all four men sink to the bottom of the lake, yet not a single man got wet! Why?

I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

John is selling fruits.
He sells grapes at $30, Dates $25, and a Wolfberry $45.
At what price does he sell fig?

PS: Logical Thinking

Using eight eights and addition only, can you make 1000?

What has many teeth, but cannot bite?