'cot' and 'camp bed' In American English, a cot is a narrow bed for an adult. It is made of canvas fitted over a frame, and you can fold it up. You take it with you when you go camping, or you use it as a spare bed at home. In British English, a bed like this is called a camp bed.
Across is a preposition. It describes the relationship between two persons, places, or things. It is sometimes used with the preposition from. Example: That house is across the street. Cross is most commonly a verb or noun. Crossed is the past tense or past participle of the verb to cross.
Therefore, up is not a preposition, and bank is not the object of a preposition. Instead, bank is the direct object of the verb held up. To avoid confusing prepositions with particles, test by moving the word (up) and words following it to the front of the sentence: Up the bank four armed men held.