As I quietly lamented (or at least noted) the impending death of GeoCities today, I wanted to double-check my memory that it was once one of the very largest sites on the Web. Yup–ten years ago, in April 1999, Web measurement company Media Metrix rated it as the sixth largest online property. Which got me to wondering: How many of 1999’s Web giants remain gigantic today–assuming they still exist at all?

That’s a relatively easy question to answer, since the Media Metrix report (which is now conducted by ComScore) still comes out monthly. In fact, Comscore released the numbers for March 2009 yesterday. So I did a comparison between the April 1999 report and the March 2009 one. Are you stunned to learn that more companies fell off the top 15 than stayed on it, and that some of 2009’s biggest properties didn’t exist at all in 1999?

Here are Media Metrix’s top 15 Web properties (ie, networks of related sites) for April 1999. I’ve rounded the figures for unique visitors up to the nearest million.

1. AOL (46 million unique visitors): Mock AOL if you must. But in 2009 it’s still a biggie–the fourth largest Web property, with 104 million unique visitors.

2. Microsoft (32 million unique visitors): Still a giant in 2009–the number-three property with 122 million unique visitors.

3. Yahoo (31 million unique visitors): It may have seen more than its share of troubles in recent years, but in 2009, Yahoo is the second largest Web property, with 146 million unique visitors.

4. Lycos (29 million unique visitors): Sold multiple times in the last ten years and greatly downsized but still around in 2009, as part of a company called Daum; no longer in the top fifty Web properties.

5. Go Network (21 million unique visitors): Disney’s ill-fated attempt to build a Yahoo-like portal remains extant in name only. Disney Online, its successor, is the 26th largest Web property today, with 28 million unique visitors.

6. GeoCities (19 million unique visitors). Yahoo had agreed to buy GeoCities in January 1999, but didn’t take control until May. Today, it’s rolled up into Yahoo’s numbers. But some time this year, it’ll just go away.

7. The Excite Network (17 million unique visitors): Once-mighty Excite collapsed years ago, but its site remains in business as part of Mindspark, a minor outpost of the IAC empire. IAC controls the Ask Network, which is the sixth largest Web property with 73 million unique visitors.

8. Time Warner Online (13 million unique visitors): Not counting AOL, which it owns today, 2009’s Time Warner network is the 33rd largest Web property, with 25 million unique visitors.

9. Blue Mountain Arts (12 million unique visitors). This once-hot online greeting card site is still with us, now part of American Greetings, which isn’t a top-50 property.

10, AltaVista (11 million unique visitors): The original hot search engine is now a sad front end for Yahoo Search, and therefore presumably rolled up into Yahoo’s ComScore numbers.

11. Amazon.com (10 million unique visitors). Still doing fine–today, Amazon’s sites reach 61 million visitors, good for tenth place.

12. Xoom.com (9 million unique visitors): Back in April of 1999, Xoom was a mini-empire of Web services, including free hosting, clip-art downloads, and more. A month later, it partnered up with NBC to become part of that company’s online efforts. Then, in 2001, it went away. Today’s Xoom.com, a service for international money transfers, is related in name only.

13. Snap (9 million unique visitors): This site started out as CNet’s attempt to build a Yahoo-like portal, then became a joint venture with NBC. And then the name went away at the same time that Xoom did. The current Snap.com belongs to the unrelated Web site preview company.

14. Real Networks (8 million unique visitors): The online media company remains a top-50 Web property today–just barely–at #49, with 20 million unique visitors.

15. Cnet (8 million unique visitors): The network of tech sites remains a big player today; in May 2008, it became part of CBS Interactive. That property is #11 in Comscore’s numbers, with 54 million unique visitors.

So to summarize, four of April 1999’s top Web properties remain in the top fifteen (plus AltaVista, Excite, and GeoCities, which are extant and part of top-10 properties). Four more are in the top 50, or are part of properties that are. Two exist but have fallen out of the top 50. And two (Xoom and Snap) no longer exist. Bottom line: If you were one of the Web’s biggest properties a decade ago, chances are high that you remain in business in some form in 2009…but you probably aren’t still a giant.

So who replaced all those companies that fell out of the top 15 over the past decade? Here are the properties in Comscore’s Media Metrix top 15 for March 2009 that I haven’t already mentioned:

1. Google (151 million unique visitors): Existed in 1999, but as a not-very-well-known startup that wasn’t within a country mile of the top 50 properties. Today’s #1 ranking includes visitors to other sites and services launched or acquired by Google such as YouTube and Gmail–also not yet around in 1999.

5. Fox Interactive (85 million unique visitors): Rupert Murdoch’s empire was on the board in 1999 with News Corp. at #31. But its modern-day incarnation is huge in large part because of MySpace, which didn’t exist until 2003.

7. eBay (70 million unique visitors): #20 in 1999. 2009’s figure presumably includes PayPal and Skype, which it picked up along the way.

8. Wikimedia Network (61 million unique visitors): I have trouble remembering life without Wikipedia, but it wasn’t founded until 2001.

9. Facebook (61 million unique visitors). Founded in 2004.

10. Apple (53 million unique visitors). In the pre-iTunes era that was 1999, Apple wasn’t a top-5o property.

11. Glam Network (52 million unique visitors). This ad network of more than 500 independent sites was founded in 2003.

12. Turner Network (47 million unique visitors): Comscore didn’t have Turner–parent of such sites as CNN.com–as a top-50 property in 1999, but it may have been counted as part of Time Warner back then.

13. Viacom Digital (47 million unique visitors): #25 in 1999.

Anyone care to guess which of today’s top 15 Web properties–which, to recap, are Google, Yahoo, Microsoft, AOL, Fox, Ask, eBay, Wikimedia, Facebook, Amazon, CBS Interactive, Apple, Glam, Turner, and Viacom–will still be booming in 2019? Which will still be hanging in there? Which will be dead, dead, dead?

Read more: