Recently I was confused by the tense usage of a text from New Concept English, the text says:
Verrazano, an Italian about whom little is known, sailed into New York Harbour in 1524 and named it Angouleme. He described it as 'a very agreeable situation located within two small hills in the midst of which flowed a great river.' Though Verrazano is by no means considered to be a great explorer, his name will probably remain immortal, for on November 21st, 1964, the longest suspension bridge in the world was named after him. The Verrazano Bridge, which was designed by Othmar Ammann, joins Brooklyn to Staten Island. It has a span of 4260 feet. The bridge is so long that the shape of the earth had to be taken into account by its designer. Two great towers support four huge cables. The towers are built on immense underwater platforms made of steel and concrete.
Please pay attention to the word I set BOLD. My question are: 1. why use "flowed" not "flows"? 2. Shouldn't we use "were built" because the bridge had been built when the author wrote this text? and if we use 'are built' to emphasize it is a fact, while we use 'was designed' in the first sentence of the second phrase?