Former Barclays CEO John Varley and three other employees are standing trial in London over charges of conspiracy to commit fraud.
It started on Monday with lengthy legal procedural arguments. Prosecutors are expected to open their case around 21 January.
The charges relate to alleged deals made with Qatari investors to secure cash injections to help Barclays survive the financial crisis in 2008.
Barclays secured about £12bn in emergency funds from mainly Gulf investors, in order to avoid the bank needing to take bailouts from the UK government.