The Aerary Porch, known as the Porch of Honour, was built between 1353 and 1354 as the main entrance to Edward III's new college at Windsor. It takes its curious name from the word 'errarium' meaning a treasury. The treasury in question was an exchequer chamber or counting house on the upper floor of the porch.

Before the construction of the present chapel by Edward IV after 1475 this porch would have formed part of the main façade of the college, overlooking the lower ward like a small tower. To either side would have stood the massive outlines of the college's great hall and original chapel (now the Albert Memorial Chapel), whose west front was set close beside it.

Despite its small scale the entrance vault of the Porch of Honour is a work of European architectural importance. Of particular interest is the vault which crowns this fabulous interior. Not only does it anticipate fan vaults in both design and structure, but its rich patterning was widely copied throughout England for the next two hundred years.

Raised above the vault is the treasury which gave the Aerary Porch its name. This is a remarkably preserved interior complete with its medieval tiles and iron window grill. At one end of the room are tall chests of drawers, early 15th-century presses for the deeds and documents relating to the management of the college's extensive estates. These chests are amongst the earliest of their kind to survive in Britain. In 1999 the documents within them were removed to the college archives but it is hoped that some will be restored to their original home after conservation work to the porch has been completed.