From the 13th century onwards this forbidden city (carry on )
has carried on (perfect?) an impenetrable existence in the heart of Africa. But to its inhabitants and thos merchants able to converge on this crossroads of the ancient caravan routes, the town on the fringes of the desert (be)
has (pefect?) a haven from the unyielding harshness of the Sahara, a place of rich grazing for cattle and camels, a university town, a revered centre of worship and a market place of both commercial and cultural exchange.
I wrotte this text in english, are the verbs forms correc in the way that i understand the text?
Can anyone correct my english?
Thanks.