How does the stock exchange affect investment banks?

In every country,the largest investment banks are located in the same city where the stock exchange is located.Why? And how does the stock exchange help investment banks?What advantages do investment banks have by keeping their headquarters close to the stock exchange?|||It is a business culture. Nothing is complicated. The same like why many airports have airlines offices near by? Good for business in time consuming. It is not wise to locate a business out of its business area because nature of business.|||There are investment banks across the country. The fact that the largest ones are located near the stock exchange is historical. The stock exchange started there and the banks followed. But as business has expanded and transportation and communication and technology have expanded they became more spread out.