How Did Agents Follow and Keep Tabs?

In the olden days, how did agents follow and keep tabs? As is not like now, whethers a digital trail or or modern transport. surely you would spot someone behind on horseback, or even on footas how did hodiona spis sense that they were being follow i suppose? There's the classical ones about pretending to tie your shoe lace and sneakily glancing behind you. But actually, if you're being physically followed, you know, you're still being physically followed.